Classic/Antique Car Repair: Cooling the engine, mustang coupe, thermastat

Question
I have a 1968 Mustang coupe with a 1969 302 V8 2 barrel engine that I rebuilt and overbored the pistons by .0030.  Ever since I put the 302 from the 1969 Mustang, the engine has been overheating. I have the same radiator that worked with the previous 289 V8 that was in the 68 but was told it would not matter if I swapped the engine or not.  Is this a radiator problem or would it help to get a cooler thermostat? Thanks :)

Answer
Tyler
HI- well the first thing I would do is to pop the no `1 spark plug and get it to TDC than remove the dist cap. it must be on the no1 plug spot on the cap if not than the dist. is in a tooth off. or the timming is off. ok and I would remove the thermastat