[King Big Ben]

I bought this car (1969 mustang coupe) fully restored and it's always had this overhgeating problem. I didn't think much of it because the engine still worked and could still get up and go when i wanted. But on a normal drive it would get from 200-220 degrees...which is alot hotter than where it should be. also, the coolant resivior would be full and the radiator itself would only be about half full.
I rescently bought a new carb (650 speed demon) and put it on at a friend's house...I noticed a big increase in power but i wasnt looking at my temp guage. i noticed a little later when i was about to drive it home from my friends house when i noticed the temp was over 240! water was literally boiling out of my coolant resevior. after spraying the radioator with a hose for about 15 min and then filling the radioator with water we finally cooled it down to about 170. there are so many possibilities; i'm not sure where to start. someone said it might be a head gasket and exhaust might be leaking into the coolant system...which does make some since since the new carb heated the exhaust so much i think it melted my spedometer cable (its badly routed over the exhaust and its happened before) which reminds me i need a new spedometer cable :)
anyway like i said i dont know where to start, so any help would be much appreciated.

thanx,
Ben