Like these:

http://www.o5m6.de/maxim_m4m.html

free standing rather than built-in to a vehicle, but made so it would fit in the bed of your GAZ trucks.  Folks could mount it on any number of things besides the truck -- kitbashed boats, modified  trains, even a sled -- and the operator could also be used with your Vietnam 12.7mm AA MG.

Count me in, I could find a use for a few of these.

Cheers,

Kev