Saw an ad for a "longtailed" TH400, would this be the same idea as a longtailed TH350 where the same driveshaft for a 700r4 could be used?

 

A long tail shaft th400 does exist but many people will tell you it's a 375... but it's not. Back in the 70's GM produced long tail 400's with fewer clutch plates in them and 375 cast on the tail housing these were weaker than the th400.
In the 80's GM started using the long tail housing again but they no longer called it a th375. I own an '88 GMC 3/4 ton truck that my friends dad bought brand new, it has an optional heavy duty 3L80 transmission (th400). It has a long tailshaft just like the 375 did but this trans has HD cast on the top of the bell housing.
It uses a driveshaft yolk similiar to the 350 and 700. It's also longer than the 700 and th350 with 9" tail so the same driveshaft won't work.
These transmissions are very plentiful in the junkyards around here. I see them in 80's to 90's vans ans full sized trucks.

 

thanks! appreciate it!