I'll be pulling out the FMX and installing a C4.

not the same. usable, maybe? if they're not rusted past the point of being able to be reshaped

compression fittings generally not sound engineering for automotive applications due to vibration. yes i've used them but checked them regularly. needing to check a repair regularly is not a good repair IMO, more like an emergency / temporary deal. using them in inaccessible / underbody locations adds negative points

MBA (My Best Advice) plan on fab'ing new lines from either copper or NiCopp with formed double flares and new tube nuts. 1 piece no connections from 1 end to the other. if you have to, rubber hose & clamps is better then compression fittings, braided hose & double clamps adds points

and FYI you don't want the tubing shaking around rattling unsupported able to contact anything or it'll wear and rub through.

losing a trans cooler line makes for the start of a bad day

don't F around with things you don't want to F around with

Of course, this is all for sound steel lines, if you have "rust belt" steel lines...

Ditto, I avoid compression fittings for any high pressure fluids, such as fuel, brakes, or transmissions.

I mentioned it in another thread about finding new lines. Most parts stores carry, or used to carry, various lengths of fuel line. I have made trans line from those, both an entire set for a car, and one or two as replacements for old lines. Those may not come in a length to reach from the trans all the way to the top of the radiator line fitting. But it's not hard to buy a union fitting, which connects two lines together. Those fuel lines have flare fittings, which are very secure, though will leak without an o-ring installed in each fitting(easy to do).

I have salvaged cooler lines before but it takes work.

At this point You can get new line and fab something, or order pre-bent lines and call it a day.

Thanks.

With respect, ATF cooler lines are not high pressure, true, but they are not really low pressure either. They have enough pressure in them to blow the rubber hoses off if the clamp is not properly tight. The problem is that rubber hoses shrink and swell with age, so the line and cooler has to have a barbed end or a large bulge. The clamp has to be tighter(smaller) than the bulge or the barbs, but still over time the hose will leak at the clamp. So that's not a lifetime parts combination, it needs attention on rare occasions. I prefer to eliminate the rubber hoses if possible, at least reduce the number of hose clamp connections.

Look into Pushlok hose connections, those are made to be permanent using proper rubber hoses made for them. Those have very sharp and deep barbs, which do bite into the hose permanently. The proper hose made for those doesn't even need to have a hose clamp, to remove the hose requires cutting it off of the barbs, carefully to not damage the barbs.