Ping at cruise speed

The manifold connections can be helped with a normal other application donut seal. People often get them from any parts store that can show their variety of sizes.

I would take the engine back apart soon, that crank wear is too much, it won't run like that for long before it creates more damage.

Are you planning on pulling the engine?  I think you got to tear into it and see what is going on before you decide what the best course of action is.  Maybe the used crank will work ok, but I'd want to find out what is going on in the lower end first before just dropping a new crank and bearings in.  If the rings and cylinders are good, you might be able to get away with the new crank and bearings.  I don't think a balancing is mandatory if you are just replacing a stock crank with another, but Rockatansky can probably speak to that. 

If you do go with a long block or a short block, you could always swap the valves yourself if you are concerned about the 2-piece valves. It's not hard to change the valves if you have the heads off.  Of course this can turn into a pretty deep rabbit hole the more you dig into this engine. 

For sure, I assumed you were going to pull the engine to change the crank.  I just didn't know if you planned to pull the engine at all, as I knew you were still bouncing around some different ideas.  For the engine stand and crane, you can probably rent them.  Or check marketplace/CL and see if you can find used ones at reasonable prices, then resell when done the job so you don't have to store them.

I am sure Rokatansky will chime in with some additional advice.  Good luck and keep us posted on the progress. It sucks that you have to go through this job, but maybe tearing into the engine and giving it a once over is a good idea to ensure it's up to the task of long distance towing.

Reusing very old stock pistons isn't a very good idea. Not many factory pistons are worth keeping, not counting super rare low mileage examples. I've rebuilt two 302 HO's using the old pistons, one whole set was fine(112k miles), and the other had one cracked piston(137k miles). The cylinders were still fine and they used no oil before rebuilding. But those were OEM forged pistons, which was uncommon in any Fords.

I'd be most concerned about the cost and machine work for a different crank, and the pistons etc.The valves of course you want to replace if possible, high rpm's caused most of those failures.

Pistons seem to cost way more than the old days, cheap end stuff can be $400 a set, while nice forged pistons are more like $600+. New pistons should mean balancing the assembly again.

Cost go up fast. $6k for a rebuilt stock level 351C is crazy. I can do that for $3k easily, they are overcharging for both the core parts, and the machine work etc. The refresh I'm planning for my 4V will be $1100ish for the roller cam upgrade, the heads may be under $400, but maybe $750 depending on the valves and wear. Mine may not need balancing or cylinder work, if it does then that's another $500. The oiling system to hit 5500 may be nothing it it's already done, plus depending on what shift rpm(5500 or 6500), could be another $400-$900(roller rockers).

the thought of a new production flat tappet cam & lifters is absolutely cringeable and understandable to not want to go there at all. and rollers aren't cheap. stick with / hold on to / reuse the current possibly 50 year old cam? i'm still on the SS Cringe. even if it's technically still good "ran well when pulled" how much time does it have left in it and will it survive being uprooted & replanted? i say uprooted & replanted because Me, if i'm pulling the donk and swapping the crank, i'm going to take it all the way down and minimum berrybush hone & ring it. rings bearings timing set that's my minimum if it's coming out. 1 washer shim on the original oil pump, freeze plugs, RTV & a nice thick coat of Ford Dark Blue. the heads are a problem, why do the crank if you're gonna let a valve drop & destroy it all? cheapest decent stainless valves, retainers & locks (because single groove vs multi groove) and a bargain valve job. i know it's starting to add up. and the damn cam. i'm still seeing older production NOS cams up for sale, lifters are a problem too. there's a Craigslist ad near me for lightweight Ford race lifters i might check out, the ad's been running forever. another idea'r popped up, Rhoads lifters may still have some quality / control going on IDK? 

i keep coming back to a saying from a wise man, "At The End Of The Day Ya Gotta Piss With The Ya Got"

and the con rod nuts. not the bolts, just the nuts, because the threads fracture out causing a failure that always gets blamed on the con rod bolts. the bolts are decent, the nuts are gahbage. cheap insurance that makes it easy to sleep at night, like the valves. why they don't sell a 16 pack IDK, maybe they do now?

check Advance Auto and any others near you for a crank kit, Advance shows a kit but won't commit to fitting a Cleveland. $332 / 50 core IIRC eliminates risk of buying gahbage from a scammer online

 

any stock replacement and even some performance valves are 2 piece friction welded. Qualcast is an entry level brand that Tim Meyer and Alex's Parts have carried, Goodson currently lists them so that says something to their quality. they have your intakes available but the X's are out of stock ATM

Qualcast on ebay w/hardware, not sure if the retainers are right for your springs though

or step up to Ferrea

FWIW all Cleveland cranks are '4M' cast code, some are 4MA, 4MAB all the same as far as interchangeability. nobody knows what the engineering changes were

Rock Auto actually has the Qualcast valves. The single-groove is stock for 1977-up 400s, or they have Qualcast multi-groove available as well. I'll just get the single-groove valves for a 1979 Bronco with 400.

Can I just leave the cam in and not worry about the cam bearings?

You can re-use the valve springs as long as they are in service spec. Measure their hieight and test the strengrh of the spring using a valve spring tester. Some guys don't like using the old springs and will swap them out with new ones but I don't see anything wrong with using anything that is still in spec.

I don't think your cam bearing will be an issue. To you would feel better changing them, then by all means replace them. Easier to do it now than later. The same with your rings. Was it burning a lot of oil before?

If thus is basically a stock rebuild, you should be okay.

Are the threads in an aluminum intake strong enough that I can put a plate on the carb mount and lift the engine that way? Or do I need to find mounting points elsewhere to lift it? I don't have the lift points that I've seen on the exhaust manifold bolts on some other engines.