7.25 Rear - Differential Interchange

you looking for gears or to swap the entire rear end? just gears, 5th aves came with 2.24's in their 7 1/4's, that would put 70MPH right at 2050 RPM ignoring converter slip with a 215/70R14 tire (a skoash under 26"), more if your tire is shorter.... a 2.76 puts you a touch over 2500 RPM @70 with the 215/70R14. >3k@65 sounds like you have a 3.55's (or 3.23's with a really short (24" tall) tire)