I myself was considering a new rear end gear setand and after doing the math, i weighted the options and i thought it would cost me about 1000 usd to do the gear change. That would include the R & P plus the bearings and seals for the rear axle and labor to install. I think i would gain 10% more crusing speed.

Now with the t-5 i would not need an adapter only a spacer and everything shoukd bolt up to the 235 motor. If i bought one from a late model S10 with a 5 speed and a mechanical speedometer it should fit real nice where my 4spd was. I would have the overdrive. This would be a nice upgrade for my 56 3100.
Those are my .02 . I guess to each is their own.

"As I lay rubber down the street, I pray for traction I can keep, but if I spin and begin to slide, please dear God protect my sweet ride." -Amen

56 Chevy 3100