727 swap

Can you build it yourself. They are easy to do. Don't need anything special to do them.

Video, ATSG manual, Munroe book and you're set on reference material.

You can build a stout trans for under $300 pretty easy, actually under $200.

Converters, I like T/A, ATI and A-1. Dynamic and Ultimate are pretty decent too. If you have a dyno sheet for the engine, even better and be honest about use if speaking with them.