My understanding is the thread on the Ford C6 is 1/8 NPS, not NPT. What’s the difference? NPT is a tapered thread, whereas NPS is a straight thread. I believe the tubing is 5/16” diameter.
I don’t know how long the lines are, but you can purchase plated steel 5/16” tubing in straight lengths up to about 60” from NAPA. These come with pre flared ends, and the flare is a 45º double flare, but it’s easy to cut the end off, shorten the tube as necessary, and re flare the end with a flaring tool. That also gives you the option of changing the flare style to a 37º JIC flare. There are a wide variety of JIC fittings available, so adapting a new line should be easy. McMaster Carr, for example has an excellent selection of JIC fittings.
With a hand bender you should be able to accurately replicate the factory lines. If you need a longer length of tubing, buy multiple lines and use an adapter fitting to join the tubes.
You can also, as you suggest use stainless steel braided lines. We did that very thing, re-plumbing some short lengths of transmission cooler lines on an Allison AT545. Amazon carries a selection of stainless hose as well as fittings. Most fittings are AN fittings. Both AN and JIC fittings use a 37º flare angle. Okay, what’s the difference? While they share the same flare angle, and they can connect to each other, the class of the threads is such that the AN fittings are made to a tighter tolerance. We have used both types on our snowcat projects without problems and transmission cooler lines are relatively low pressure. You shouldn’t have any issues.
That said, there are different types of braided stainless steel hose available and you must get fittings that correspond to the hose type you select..
