I swapped my Turbo 350 for a Super t-10. I just finished replacing the U-joints in the driveshaft and went to install it and it appears to be 1/4" too long. I've never had this driveshaft installed with this transmission and the rear end is an 8.5 10 bolt also new to the car. Am I missing some trick to get this in?

The difference is because of the rear end, not the trans swap. Muncies, Saginaw 4 speeds & 3 speeds, T10s, etc are all the same length (including bellhousing) as a short tail TH350 or a Powerglide. I believe there is a rear end yoke available that's slightly shorter you can use to make it all work without cutting your driveshaft. Someone with more experience with this swap can tell you.

Just make sure your rear end is under load (if the car is on jack stands make sure the stands are under the axle). and not just hanging, that might give you the extra space you need to install.

The difference is because of the rear end, not the trans swap. Muncies, Saginaw 4 speeds & 3 speeds, T10s, etc are all the same length (including bellhousing) as a short tail TH350 or a Powerglide. I believe there is a rear end yoke available that's slightly shorter you can use to make it all work without cutting your driveshaft. Someone with more experience with this swap can tell you.

Close but not Totaly Correct. Early small output T10,s are the same length as a Muncie/Saginaw/3 speed etc, BUT a large yoke 1974 up Borg ST10 is 3/4" longer, the same as a later model big output Muncie from 71 up.

While I realize that this is not exactly the same, I made an error several years ago when I swapped in a 8.5 rear...my driveshaft appeared to be too long, so I took it and had it cut down an inch...

The rear was not on jackstands! when I put the rear under load, my driveshaft wa sabout an inch too short (not a lot of yoke on the transmission output shaft)...while it worked out in the short term--I ended up needing a new driveshaft--

Measure twice, cut once--ONLY IF NEEDED!!!

Thanks. It's not on the jackstands. I'm gonna give that a shot.