OK ill rephrase that.

The input shaft is the same, but the bell housing has bolts in a different spot since it went on a different motor.
the 3t was mated to the 18R motor, whereas the 2t went on the 4k motor.

the bolt pattern on the belhousing is different, the diameter is about the same.
the internals are suposed to be stronger on the 3t box, but there is not documented evidence other then opinions.

there was 3 different versions of the 3t box, of which they differed mainly in the length of the shifter casing. they got progresivly longer over the years, about 6" difference between the longest and shortest version.

There was also a range of different gear sets available, but that was an option so most are the same gear set, accross the years.

The split caseing in the midle is identical between the 2t and 3t i am sure, but some more research on this is forthcoming.

perhaps i should WIKI this... ahh any objections?