Have you tried out how the Warlord/Pro Gloria plastic pikemen mix with GW bitz?
I've sot of tried it, there are pics in an earlier post in this thread. Edit: No there aren't. Where did I post those pictures again?
Anyway, my verdict is that the 6th edition multi part soldier plastics, along with a couple of bits from the more recent archer kit are the only GW bits that work together with the Pro Gloria plastics. The 6th ed plastics were sculpted by one or both of the Perry brothers, IIRC, so not that much of a surprise. Everything else looks goofy and mismatched.
These arquebusiers are metal though.