[M2M]

Originally Posted by Purdy Swoft

I see the later Bud wheel and a C head.

Originally Posted by RUNNERBUN

Timing cover is also Model B. Timing pin has the elongated boss.

Yep, most of these GAZ trucks were fitted with B blocks from the mid-1930s onwards although A blocks kept on being made and fitted. The B block trucks are referred to as GAZ-MM.