[El Dorado Jim]

I would stick with your bulletproof 400, they are awesome, change to a higher gear rear end if you want the engine to run lower rpm's.....would be cheap, pick up one for a few hundred bucks.... and like others have said, the 700R4 wouldn't hold up, I have checked into that for my '73 Suburban with 454,with t-400, I have a 4x4 so am keeping my 4:10 gears but going with a gear vendor, very expensive,but I bought a used one and now have to buy the adaptor and install it.....thought about the 4l80E but way too expensive!!!!