Depends on the four speed that you're dropping in- if you're using a '66-'67 833 which has a 26 spline output shaft, it's a drop-in.
If you've got a '68 and later four speed, you'll need to swap to a 30 spline slip yoke.
This is all assuming you're installing an A body four speed...
Most A-/F-body aluminum overdrives are also 26 spline. A 30-spline aluminum short-tail is a rare bird, but they were made. The only 30-spline A833ODs I have are a cast-iron case, high-helix '75 A-body and a couple of truck transmissions.