I've had a set of NOS 3.55 gears for a 7 1/4 for years, thinking I might use them someday, but eventually found out this particular gearset only fits 60 and 61 (ring gear bolts are smaller), so I can't use them.
Sometimes you eat the bear, and sometimes the bear eats you.
I'm gettin that dana power lock sure grip rear end from Roy with the 3.90 in it. Mine has a 2.93 in it now. It oughtta smoke um from a roll with that thing.