Since the model will be 100% metal and green stuff, I'd use acetone instead. Simple green is only good because it doesn't dissolve plastics. For metals, dunk it in acetone for a day, scrub it off with a tooth brush. Then take a little bit of Winsor and Newton acrylic brush cleaner and clean all the remaining primer in the wee crevices of the model.
I've had models dunked in simple green for a couple of months now (I received a bunch of Tau from a good friend), and after several scrubings I still can't get rid of all the primer. I'm considering using some of the Winsor and Newton acrylic brush cleaner on them since technically it should be safe on plastics, but I have yet to experiment and the cleaner is a little pricey.
Should I do a painting log?