The '58 1/2 ton had two rear end ratio options, 3.90:1 and 4.11:1. The 3.90 is the most common. You'll have to check to see which one you have. The S-10 T-5s are commonly .72 or .78 OD, but there are a number of other ratios. Check the tech tips for a lot more T-5 info. Having said that, the 235, T-5, stock rear end seems to be a good combo to me.
best wishes,
Les
