The E4OD is considerably larger than the AOD and requires the computer to shift it. The AOD (with a 157 tooth flywheel housing) is the smallest and will fit quite well, this is what I run. Some notes about the AOD
-Throttle Valve (TV) linkage must be set accordingly or you could wind up killing it within a mile
-Usually the first thing to go in an AOD is either the OD band or the smaller input shaft. The input shaft will sheer when the transmission is shifted from 2nd to 3rd or 3rd to OD because this is when the engine's load changes from the outer shaft (from torque converter) to the inner shaft (direct torque from engine). The '88 and older tailhousings have extremely poor lubrication and should be changed to the newer style if running 3.55:1 gears or higher. Also, the AOD has a shift pattern of 1-D-OD (which sucks) and the E4OD has 1-2-D/OD I believe. If you do infact have an AOD I highly recommend a LENTECH VALVEBODY. I am extremely pleased with mine and it eliminates most all of the AOD's flaws including changing the crappy 1-D-OD shift pattern to a more user friendly 1-2-D/OD. It also allows 3rd gear to be completely driven off of the outer shaft so you don't have to worry about harsh shifts sheering the inner shaft.
