The longer tranny is a 727. The shorter is a 904. From the factory the 727 is the heavier duty tranny but about 3 tenths slower in the 1/4 mile. The 904 is typically a slant six/ 318 tranny. However, the 904 can be built to withstand the performance you want to give it. If you are just going to do a cheap "300.00" rebuild, then the 727 may be the choice just for durability if you plan to "hot rod" around. If the car will only go on cruises, the 904 is a great choice. If you are going to "hot rod" around, the 904 is a great choice but maybe a little more money on some performance upgrades to withstand the abuse. Yes, the balance flexplate is the way to go because then you can use 340 and 318 converters. The use of the car and how much money you plan for the tranny will be the deciding factor on which tranny BEST fits your need....
