If your not changing the tranny then it is is not relavent which tranny you have.
When I swapped the 7.25 to and 8.25 I had the drive shaft shortened 1.5". It's easy enough to check though. Put a piece of broom handle in the u-joint saddle on the 7.25 with it parralell to the axle tubes and measure from the center of the axle to the center of the broom handle, then do the same on the 8.25. Subtract the 7.25 from the 8.25 number and that is the amount you need to shorten it.