Hy p.dow, GM changed the car frames in 58 to an "X" design, to work with this frame change, the tranny was shortened, and a mount was added to the shortened tailhousing. I believe the trannies are the same up to the rear of the main case, but the car tranny is definately not the same length as the truck tranny for the 58 and 59 model years, hope that helps.
