I am running an older copper core radiator. Its very large. It is probly 30 or 32" wide. I think its 21 inches tall, I measured it but I'm not sure.

I have had some cooling problems in the past.

On hot days, it runs hot and I can't idle for longer than 3 or 4 minutes. I have a 160 degree stat in the manifold.
I want to change over to an aluminum radiator. Does aluminum radiators,(besides looking good) cool any better?

If a very large copper core radiator is marginal, what size aluminum should I get?

I run a Moroso water pump on a BB Chevy with a pretty high lift cam. I have a mechanical fan too.

I don't want to get too fancy, I care about looks but not that much. I've seen some radiators in Summit that are 6 or 7 hundred dollars. I don't really want to spend that much. If I could get away with 3 hundred that would be better.

what kinda car?
I don't think a radiator that big would fit in a firstgen, standard ones are 17" tall by 28" wide or so.
The summit brand alluminum radiators are a good value, they are made by Northern radiator and priced around $300. They come with the right brackets for direct bolton in many cars.

Other things worth checking include do you have a full factory style shroud? It won't cool well without it. Are you using a good 5 or 7 blade clutch fan, if so is the clutch good? Are you using a cheepo flex fan? Most of the cheapies do not cool well at all. Derale makes some good flex fans that move a bunch of air.

Depending, you may get what you need from just having your existing rad cleaned out or recored.

Its a 1967 Camaro. I measured from side to side, over all length. That included those resovoirs that are for the auto trans lines to hook to.

The fan is a metal, non flexable type. I used to run an electric fan but the non flex, metal one that is not on a clutch and just is belt driven from the crank pulley cools so much better.
It is about 1/2" from the radiator.

Also, the way it is installed, it is using smaller tie wraps for connecting the bottom to the radiator support. The top is using a piece of sheet metal to connect the top to the rail.

metal one that is not on a clutch and just is belt driven from the crank pulley cools so much better.
It is about 1/2" from the radiator.
As Jim mentioned Shroud ....having the fan that close to the radiator, puts it inside the shroud, and decreases fan effiency. The fan has to be just inside the opening of the shroud..this prevents 'air spill' of the end of the end of the fan blades....Have a look at the case/cpu fan in your computer as a example.
As also as Jim meantions...u may have flushed/cleaned the radiator, this is just scale, it doesnt unbloke cores that have been that way for a long time, or bloked because of broken bits off the bottom hose, interal support coil.
Send the radiator off to have tanks removed and cores manually cleaned.
A rough check...(and it is rough) for bloked cores.
From cold, and as the engine warms up, run your hand over the cores, at the lower hose side, often u will feel a core (usually low on the radaitor) that is colder than the rest