I was told the 4 cyl ones and the 4.3 ones had Bronze bushings on the counter shaft in the case. The v-8 ones used actual bearings. The extra torque on the bushings egg shaped the case holes and the gear teeth did not engage as far and then eventually broke.You can have the case bored for bearings but it is not cheap.Some of the Transmissions are rotated slightly to clear the floor pans on some vehicles. If you get one of these the tailshaft has the shifter offset so if you try to install in normally the shifter is at an odd angle. You then have to find another one with the tailshaft/shifter in a location you can live with. I don't think any of these original equipment trans. were very tough.You can adapt a T-5 or T-6 from another type of car but they are very pricey also.
One other thing, up until the mid 90's they all (to my knowledge) had a slave cyl mounted on the bellhousing for the throwout bearing.They changed to a hyd. throwout bearing in the later ones. As far as I know none of these transmissions had a mechanical linkage for the clutch.The hyd. throwout bearing uses shims for adjustment and is pretty complicated to get it set correctly without tearing it back apart several times. Hope this helps.
One other thing, up until the mid 90's they all (to my knowledge) had a slave cyl mounted on the bellhousing for the throwout bearing.They changed to a hyd. throwout bearing in the later ones. As far as I know none of these transmissions had a mechanical linkage for the clutch.The hyd. throwout bearing uses shims for adjustment and is pretty complicated to get it set correctly without tearing it back apart several times. Hope this helps.