LTDII AOD conversion?

I know the flexplate in AOD is same number of teeth as my C4, but I'd have to use the lighter weight C4 flexplate in the AOD, as well as my starter.

I have found AOD conversion kits for 351M so it will bolt up to the block.

What I don't know is what other modifications would be required as far as driveshaft length and if any modifications are required for the transmission cross member or if it will work as is.

Right now I'm in the midst of a frame off restoration.

the crossmember should be the least of your problems if there are multiple hole locations in the frame mount tabs,

or both transmissions may even use the same crossmember location?

i would calculate driveshaft length when you have both transmissions and the adapter kit side by side. the AOD will also need a 31 spline slip yoke.

i'm pretty sure you'll be shortening the shaft so just a cut & balance, swap the yoke w/ new joints will get that done.

the flexplate needs to do 4 things right; tooth count, balance weight, converter stud bolt pattern and offset

you're correct in that your C4 should be the same 164 tooth count that the AOD uses, the balance weight for your 351M is 28oz-in same as 289, 302 before 1985, 351C, 351W and 400. they all use the same weight except 302 when it went to 50oz-in in 1985 IIRC. the 2 you need to work on are the converter stud pattern and the offset. C4 usually uses a 10.5" stud pattern while the FMX, AOD & C6 usually use a larger 11.5" or 11 7/16" pattern. you'll find them listed either way, they are essentially the same. from what little i remember the C4's use a different offset than the FMX, AOD and C6 but some say if everything else is right they'll swap, IDK.

i would go straight to an FMX / AOD 164 tooth flex for a 351C, 351M, 351W or 400 engine for a 99% fit

personally i'd also skip the adapter plate and move to a 351W rather than replant the 351M,

unless you're upgrading it to a 400 internally? the 351W is still correct to the H vin code.

or if you're interested the 351M can be 'corrected' to perform on a decent level, that means over-all efficiency not turning it into a pig ... sorry but they already have that covered. the issue lies in the lack of both static and dynamic compression ratios, barely 8:1 with retarded camshaft timing doesn't cut it, it can be corrected 

same kit for less? Monster probably drop ships from PATC

but like i said, for that $ i'd go a different direction, maybe even an FMX engine block

I am keeping my 351M, not that I'm in love with the motor because there's nothing easy about it, but it's the motor that came with the car, and this is kind of a special car. I got a 400 crank for it and will be boring it out to make it a 408 stroker. Fixing the retarded cam timing and some dome pistons (I'll need the 400 pistons anyway) can bump the compression up. Ford Muscle did a nice article where they made a 468 ft-lb torque and 380 hp 400 for $2000. It no doubt will cost more, but I've been following this plan for mine.

ANYWHO, I need to decide if I want to go through the insane PITA and expense to switch out to an AOD. I drove this thing all over hell with its C4 but it only has 2.75 in the rear, and that really needs to go. However, on my 67 Mustang with 14" tires and 3.55 in the back, it's not fun taching 3000 rpm just to go 60 mph with a C4.

Hemmings has a nice article on the swap in general.

https://www.hemmings.com/stories/article/ford-aod-overdrive-transmission

with a 408 i'd go with a C6


technically not a stroker, the 400 came with the 4" stroke crank, same block & heads, you're just upgrading from 351M to 400 with a .030" overbore to make 408 and no M because it's a 400

or you could say it's a 351M bored & stroked to 408. then it would be a 408M i guess

but anyway, no ing way a C4 is going to hold up behind a 408 unless you baby it. even then you should have enough low end TQ to hurt it bad and i still worry about the FMX / AOD platform. the low end TQ is why i'm having a hard time jumping on the wide ratio bandwagon. true the LTD II is a sled but the 408 should be able to handle it easily. you can get the low ratio planet set in a C6 too, run even a 2.75 or 3.00 gear and it'll be no slouch coming off the line, then when it's in 3rd / regular D range it'll still be right for the mph

another direction is a std ratio C6 and Gear Vendors OD

big car, big motor, big transmission

I considered an OD transmission, but too much hassle/money with the bell housing issues to run a AOD with the 351M/400 since it uses the 385 series bell housing. On top of the cost of the bell housing, a high performance AOD build is pricey compared to a old C6.  So I had my C6 rebuild with a Broader kit (std gearing), for a fraction of the cost.  In the long term, I'd like to go to 3.25 gears and a Gear Vendors OD, but that's a big investment.  I think that'd be the ultimate setup for my car, giving it a big more snap off the line and and also lower the cruise RPM, but for now, it's great as is.  

If you can't afford a GV OD or don't want the hassle of trying to adapt an AOD, consider just running a C6.  With a built 408 it will run fine and cruise RPM will be okay with the proper rear gears.

For the AOD idea, also keep in mind the AOD is made for either a carburetor that has the proper AOD TV linkage on it, or the common Fox Mustang throttle bodies. Attaching the TV to another carb is not that simple or easy.

The ideal trans is a 4R70W, and a stand alone controller, but those can be $400 or were a long while ago. I'm working towards an Explorer(late 1997) 302 system, the PCM and wiring harness. That'll run any 302 and 4R70W base, other engines would need a special distributor modification(it's a cam synchronizer in those(DIS)). So I'm debating on a 302 or a 351W based block engine(big price difference). Then the transmission is a straight forward deal, work out the shifter, drive shaft and mounting.

Perhaps I'm biased, but I agree 700%. I have a 67 Mustang Coupe, a 69 Mach 1 428 SCJ, but this is my favorite of them all. The sentimentality to it probably helps that, but even in highschool, I loved these cars. 

As a freshman, there was a kid in our school who had an Elite and I loved that car because it reminded me of our LTDII we had when I was a kid. Little did I know in just two years I'd get a chance to buy that very same car back from the guy dad had sold it to about 10 years prior. So I did, and it was my car through highschool and college.

I was more going for lack of complexity in C6 vs AOD or 4R70W.

Along with "lack of complexity" the C6 won't need to have an adapter to bolt up to the big-block trans pattern. 4R70 controllers and wiring were in the neighborhood of $800 a few years ago, add a trans adapter, rebuild costs, driveshaft mods, and maybe flexplate/torque converter costs as well...

Cheaper/simpler to use a 351W, or get a Gearvendors add-on overdrive for the existing trans.

I agree, I had the pricing of the 1200hp C6 in my head. At $1700 for the wide ratio package, I don't think the local shop can do it for that. It costs about $900 to get a new rebuilt TracLoc chunk from several vendors on Ebay, and they can't do it for that either.