Marvin with a 9 in his right, .45 in his other hand

This is Marvin's left hand modded so it can accept a gun in that hand too.

Needs supports, I'm not fancy like that.

You will need to remove the tab on his left arm using clippers and just glue the left hand on, I couldn't get the configuration to work well enough to utilize the tabs, as its a tight fit with the gun placement.

Be sure to add the gun to the hand before glueing the whole thing to the body.