I suspect it's possible but you would kill what is already a lack of painful acceleration. It would be a great time to consider a 700R4 overdrive transmission. Four speeds instead of two and an overdrive capable of not only increasing performance but also fuel economy.
Yes, but you would have to change carriers.
Different carriers were used for 2.56 and 2.73 gears than for 3.08 and lower gears; because of the large diameter of the pinion required for the higher ratios (2.56/2.73).
I have a '70 with an 8.2" rear end and 2.56 gears. If you might want to consider a carrier trade, send me a PM. I'm on the other side of the fence: I don't care about cruise RPM; I want more response off the line.