[Sid]

If you decided to go with a straight 3 speed and assuming your car may have 3.31's and you don't live in the mountains you may be okay. No need for overdrive and solenoids either. 3.55's would be ideal. Tire size would also play some roll. With 225/70/15's and 331's you would be at about 2650 rpm @ 65 mph + or -. O/D tranny is nice but a direct 3 speed is an easier conversion without dealing with cables & solenoids etc. I have a F1 ford with a flathead 3.25 rear 235/70/15 tires and works great on take off and top end. FYI diff. carriers 49-56 interchange. 55-56 you my need to use your spider gears or use the later axle as spline count is 28 on the later. Going higher # numerically should not be an issue in your housing if you choose to go that way,