After some encouragement here I've decided to try and build my first trans and picked up the step by step "how to guide" for the 727. Then I saw this and wondered if anyone has tried it and if it fits as easily as they imply. How it holds up. And a four speed wold be nice without having to cut the floor.
You can install an A518/A500 in a B/E body without cutting the floor. All you need to do is trim some of the stiffening ribs on the tail end of the trans, and make a trans mount. I designed my own and fabbed it up from plate steel. I can help if you need me to. I still have the pattern somewhere.
You also need to change over to 1/2 cooling lines and cooler from the factory 3/8 lines.
You will need to address the controllers but thee are several options already out there.
I say rebuild it. Chrysler's are one of the easiest trans to rebuild IMHO.