Rear end swap

The 7-1/4 in my '73 Duster was replaced with an 8-1/4. The axle tubes are smaller on the 7 and the springs were narrower.
Your going to need new U-bolts and a shock mounting plate set.
I would not go with S/S springs. The height would be raised alot. (If thats OK with you) But would rather do a mono spring set up from cal-trac and there bars together. IMO, That would be your best bet hands down for going fast and straight.
Weld in the frame connectors. Bolting them in is oK, but they will wear out. (AKA, ob-longing the holes) A removable set is more of a pain than it's worth. No casual looker will ever notice they are there.
A set of BFG drag radials or the like tire will do you right.