I'm going to throw something out here, just as an option to consider.....
How often will you drive this truck on the street? Really, what I'm asking is do you really need overdrive? If not, you could do a TH400 3speed. That trans is significantly cheaper to build for big horsepower, doesn't need the controller, and doesn't need a lockup converter. But this would be a pretty much race only setup. With no overdrive, you'll spin the motor pretty good to run down the highway at 70mph.
So, basically you've got 3 options:
1.) Put a 700R4 in it, hope it stays together, throw money at it when it breaks (not if, just when). Least amount of money now, but also the least reliable and most unpredictable.
2.) Put a TH400 in it, don't drive it on the street as a daily driver. More money than the 700R4, but less than the 80E. Will be plenty strong, but you loose driveability.
3.) Put a 4L80E in it, drive it wherever and whenever you please, and don't worry about breaking it to speak of (its possible, but pretty hard). Yes, you'll spend a fair bit of money now, but it'll be the only way to make it a reliable truck that you can run on the highway without running 3500rpm at 70mph (my guess).
That pretty much summarizes the options. None of them are great (the 80E is a great solution but hammers the wallet pretty good) but that's the way it is. You've got to pick the option that fills YOUR needs the best. And maybe you need a running truck now and don't have the $5k (or whatever the total is) to drop on an 80E. Only you can figure that out.
'JustDreamin'
