the stock 3.90 will handle lots of power - friend of mine has a 55 w/ a strong 427 and he's a lead foot, no problems with the stock rear
the TH350 is good, TH400 fine too [supposed to be stronger], and it'll all fit easily .... depending on what you intend for the truck, you might want to consider an OD trans of some type [OD automatics: 700-R4/4L60 or 4L80E] to get highway speeds with lower RPM, but if it's an ocassional driver not on the highway much, the 350/400's will be cheaper and easier to find ... but I like clutches
you'll find lots of good advice right here if you run into any puzzles! :hammering:
Bill
