Don't know if I need to mention this or not, on the subject of driveshafts...But, when I used my exsisting full-size 1996 GMC/Chevy truck driveshaft, that was in the the original 4.3 Litre 4L60E...and put it in my new 2001 F-Body 4L60E tranny, it leaked all the tranny oil out of the end of the input shaft due to there being a hole down through the center of the input shaft, which I guess they all have(?). After some research, I was told to silicone in a beer bottle cap down in there over the top of the hole(by a transmission shop, no less). It actually fit perfect. But I don't like jerry rigging things like this & will weld the hole shut. Evidently, the F-Body driveshafts don't have this pressure relief hole, OR...The F-Body tailstock does not have oil in it. Don't know if this applies to your situation...

Gar