Hey guys, I have a 1963 Chevy C30 Dually that I want to swap the ring and pinion out of. We did the "turn the tire twice and count how many revolutions the driveshaft makes" and found it has somewhere around a 5.13 gear ratio in the rear. The truck motor screams at 4,000rpms at 70mph. I want to buy a set closer to 3.23 that will take the rpms at 70mph down to a more acceptable 2500rpm. Trouble is, my dad swapped multiple rear ends in and out of this truck back in the 80's and has no idea what rear end it's running now. I found a stamped number of 3766686 with a "D" under it on the rear end but haven't had much luck with google searching. I would like to order a gear set on Amazon if possible. Any help is appreciated. Thanks in advance.
*I've attached some pictures below*