[Jason Abbadon]

AIM goons would work great- as would the WWII Cap or the Hydra soldier (from the Cap line).
I'd go with the basic Spidey/Madrox body and head with a bit of Aves sculpting for hair...or use a Havok head.

Good luck- anything we can do to help, just ask- ad please post pics as you go! This sounds like a great first custom- and best of all...no one has done this character yet!
No matter how it turns out, it'll be the best damn 3.75 Rusty out there!

I wish they'd bring him back to life somehow- maybe an AoA badass version for X-Force!