First off, the car and truck rearends are similar but will not interchange, all truck gears, misc internals etc are slightly larger. A pumpkin from a late 50s truck may bolt in, however ratio choices are limited. You'll need to weld saddles on your original axle housing anyway so the whole thing doesn't flip over (the torque tube used to keep it from doing that). So, might as well go with the next generation truck rear end and have a much better ratio selection. I'm running a 1966 half ton unit under my 46 pickup which fits perfect. One more thing to consider, if you will be running an overdrive trans you could get along just fine with a lower ratio rear end, say 1957 pickup with 3.90s. Best of luck.
