Looking for some Differential advice

All this advice is worthless since you left out some key points. One of the biggest is, what size tires do you have and what size do you plan to change to, if you change? Tire height has a huge effect on final gear ratio. On my 64 for instance, I am still running the stock height 13" tires and I have 3.23 gears behind a slant 6 and it is very peppy. I am extremely happy with it.