Below are two variants of the GM (or otherwise known as the “Jim”) Gundams. One is the twin cannon variant and the other is the grunt/cannon fodder version that usually gets killed off right away.
Stilll image of RGM-89 From Char’s Counterattack
This still image is from Gundam 0079. I believe this is the one I have
Below is a later varient from Gundam Z/Zeta Gundam with just one cannon