Hmm, forearm does look a little short, might be worth considering adding a section to the hand/small end, either fixed on or a bit like a bangle?
Maybe work out how much you need to enlarge your chest peice and see what effect cutting the whole under arm/rib section out, adding new to where it was then re attaching it so it takes it away from the body?
Mighty fine bondo work there, would be a shame to start over, and some very cool guns by the way. Impressed