The '60-'62 1/2 ton used an Eaton posi with 3.90 gears. I beleive the code on the axle should be MU. The '59 used the GMC Spicer 45 axle for the posi option, with a 3.92 gear. I have the manuals for both years and have done some research on thae posi Eaton 1/2 ton rear. It's a very rare part.
