Re: 12 bolt rear end: posi?
A couple things:
3.73's would be great with a 700r4. If you have 2.56 gears AND an overdrive, it will possibly bog the engine at normal highway speeds, giving you worse fuel mileage. The 0.7:1 overdrive will make cruising a 3.73 almost exactly like a regular 3 speed transmission cruising with a 2.56. (3.73 x .7 = 2.61 )
Also, if you have (or acquire) a posi unit that is a 4 series carrier, most ring and pinion manufacturers make a 3.73 gear for 4 series carriers.
flat top 406, AFR 195's, XR286R, RPM AirGap
750 Holley DP,TH400 w/brake, 4000 stall FTI
3.31 gear, 12 bolt
... for now.