Something to consider, changing to a overdrive tranny will lower the engine rpm,but the rear end will be turning faster and may fail. Lots of 10 bolt rear ends are available and 3.08 gears work well. The engine rpm is lower and the reared is not over stressed. Just something to consider.
That is what I did and it dseems to work well.
The rearend will not be "turning faster", it will be turning the same speed as it would with a 1:1 trans gear at the same indicated speed. The engine rpm is the only thing that will change. The only way the rear end will be turned faster is if a higher road speed is run. The stock rearend will hold up fine, I run mine at 70-80 mph regularly, and have had it faster than that.
The 3.55 gears available are not for the '55-'62, they are for the '47-'53 torque tube differential. Only aftermarket gears for the '55-'62 are the 3.38s.
