It seems that the Soviets prioritized tanks over trucks or other supply vehicles during the war (or couldn't set more production facilities for them).
I think that there is a more straightforwards conversion/basis than tanks themselves. The SU-76 SPG already features a front mounted (or two?) engine with the driver at the front.
Remove the superfluous ammo and gun, extend the superstructure as much as possible, maybe add some form of armored roof, crude seats and maybe a simple hatch with a pintle for a MG and you get a very simple APC, although it probably won't carry many people.
A more durable design would be a stretched SU-76 with one or two extra roadwheels (maybe not necessary), a reinforced suspension, a stronger engine, revised driver's compartment and more space for a full 7-10-man squad. The Romanians designed an APC on the SU-76, called the MLVM.
Note that in 1944 or so the US started development of an APC based on the M24 Chaffee.