The ONLY reason I would use an 8.8" rear end is if I were putting it into a fox body, since the control arms physically bolt up to it and it has provisions for a speed signal for the computer. The friction horsepower consumed by the 8.8" should not be that much different than a 9" IMO, since the gear area is somewhat close. You cannot easily change gear ratio's with an 8.8" and the axles are held in with clips. You have to drain the gear lube and remove the rear cover to get at them (or convert to a 9" axle retention plate). You also cannot lighten one up using aluminum components like you can with a 9" (or an 8"). The 8.8 also can be VERY noisy, requiring bolting on a large hunk of iron (heavy) to tune the noise out of the cruising range. My 2006 Mustang GT's rear end was so noisy that I had to take it back to Ford twice before a TSB was released that introduced a dampener (guess who had to pay)? You can probably see that I don't like the 8.8", yet I am swapping one into my 86 T-Bird because it is easier.
