OK... Looks like a very late '60s Italian made Masi GC to me. Possibly as late as '72 or so... This was really found in a dumpster? I'd like to see more pics...!
Anyway, the M61.5 looks to be the frame size measured from crank center to the very top of the seat lug; you can check that. If no other #s on the BB shell, then you'll want to pull the fork out and look for #s on the steerer tube. Let me know what you find there. Looks like the bike has some interesting parts on it... Aluminum crank bolts? Weyless seat post? Do the Campagnolo brakes say Campagnolo on them? Is that pedal a modern "egg beater" type? Pretty cool dumpster find...