I've never heard of "12.5 x 20" tires. Did you mean 14.5? Because the M35A3, stock, used 14.5R20 radial tires that are ~43" tall vs the 9.00-20 NDT's that are about 40.5" tall. Though correct, they do only add 1-1.5" of ride height.
The following figure I found here on Steel Soldiers and it is oft referenced.
View attachment 638682
Sorry,
I don't know where I got the 12.5 x 20's being on the A3, they're 14.5 as you said Val
ence. But there are 12.5 x 20 mil tires out there. Here's one SS link. I've seen them too. Honest.
http://www.steelsoldiers.com/showthread.php?7976-tire-sizes