yes it is the spacing on the lower tranny bolt holes - 12.5 is a narrow block, 13.25 is the wide block measured center to center of the holes. I was under the impression that the 2 trannies were different lengths because of different amount of gears - good to know they are the same. Actually, the 4 spd ia the rarer of the trannies for the 2.0 motors, as most of the 2.0s after 82 came with 5 speeds, except for the total base truck.