3/4 ton axles or 1/2 ton axles on 72 Blazer

[SeventyOne]

That's a tough question to answer.

Need to know the tire size you want to run, the transmission you want to run, and what is an acceptable RPM (in your opinion) for highway speeds, be that 55mph or 75mph or whatever.

You said you want 20" rims and low-pro tires - right? So would the tire height be 24" ( as a guess?) then 4.10 seems too high (numerically) for your application.

Most people with 4.10s will be running 33" to even 36/37" tires.

Once you know all these answers there are gear ratio calculators that can fine tune the right number for you.

I would guess a 3.08 might be right on the money for you.