I've got a 54 Powerglide rear end in my 37 truck. You'll like how much it will help your truck - especially on the freeway.
Be sure when you look in at the notation in the Chev's of the 40's catalog that says "all", it doesn't mean all TRUCKS, which is what may have happened to you. I would specifically get the parts you need from the Chev's of the 40's CAR catalog.
All of the torque tube parts interchange between cars and trucks, but you cannot use the car torque tube retainer ring because, at least on the 54 car, it has five holes to bolt it to your stock tranny and all you've got is four holes. Use all of the parts from either, but you'll have to use the truck retainer ring. I think I sent you the article on this swap, and you'll probably remember the other area that is tricky is the u-joint. Your 40 may have the 17 spline u-joint, and if so your OK. If not, you will have to mix the u-joints using the truck 10 spline and the car 17 spline.
Hope this helps!! Good luck!
Joe
