OK, I think this is the one
http://www.ebay.de/itm/Flakpanzer-M2...item27f7cdd125
I have two of the torro M16 halftracks with that same quad .50 set-up and just last night I was thinking about pulling the quad .50 out of one and making it into an M3. Rex, if you're serious about building one of these flakpanzers maybe we could work something out for the quad .50 parts, or maybe you'd be willing to give me a little guidance (not the first time for that

) and I could try my hand at doing a flakpanzer. Especially if you do a build log on yours so I can flagrantly and shamelessly copy the efforts of someone much more talented than I am.

Maybe even get myself one tiny step closer to being a scratchbuilder.