My K-5 is pretty close to a mil spec blazer.
The mil specs had a Th400, Np208 and axle gears of 3.08:1.
My K-5 has an SM465, NP208 and axle gears of 3.08:1.
The Sm465 and Th400 have basically the same gears, save for you shift one manually. Only difference now is mine has the Banks kit on it.
I can get between 18-22 out of it i'd say. I've never sat down and did the math though.