Overheating '67 Cat

Hey guys and gals, I'm new to this forum thing, but my 67 cougar is having some issues I thought you might be able to help with. its a 289 and after i came home from kansas she started getting hot really quick. I replaced the thermostat, which helped the pegging on hot problem, but she still heats up WAY too quick. Now that i've backflushed the radiator, she's spewing coolant before her temp gauge goes half-way. I know the gauge is ok, i tested that. Also, talked to a few mechanics to get their thoughts and got mixed answers...head gasket, heater core, need a shroud...Anyone have any thoughts. I'd like to diagnose before i just start replacing things.

Thanks,
Katrina