I took a stab at a creating
a damage system tied to log ST a while back. It's here if you want to look at in for ideas.
The effort to work in armor is interesting but I think it might be simpler to come up with some way of combing Armor Value and Toughness for a single value. I tried to do that in my system but I'd probably change how I handle cutting and impaling damage.
I think it might read better if you started by laying out your system and after that how to convert GURPS values to SOLIDS. But that might just be me.