IMHO, Nothing comes near the 3 08, even if you swap to a 5 speed. Have done both. I tried the 2 88 as my friends, the gearing is a dog off the line, so much so, its to me dangerous with a 4 speed car. Also when shifting from 3 to 4 th it almost bogs the revs don't keep up.
Again, IMHO and you know what that means.......
My 1970 triple su, electronic ignition, Dayton 6 inch off sets, and a later xjs VENTED 3 08 rear will convert your car into a wonderful GT .
Your gas mileage will hang around 28 mpg if tuned right. Oh yes the gm one wire alternator as well
You will not regret the 3 08.....the 3 54 is horrible .once you switch you will see.
Goog luck , need any help just pm....I average 6,000 miles every year in my 70, see you at Indy, Daytona or Import Carlisle.
GTJOEY1314.