OK, assume you read the "Sticky" in the Tech section on overheating. Several times on these forums it has turned out to be the water temp sensor as the "generic" ones from your local parts store seem to give a false reading when in fact your temp may be OK. Getting one from a Pontiac parts supplier will get you a good one. Simple checks are to make sure the fan is not to far from the radiator, use a good flex fan and fan shroud (this improved my cooling), and use a 160 T-stat (We have had a number of owners say the "new" T-stat was bad and when a good one was installed, temp was good). No doubt you read about the water pump and plates as being a problem as well.
Ever try throwing on your heater on high when it starts to climb? This may burn you out of the car, but can work as the heater core acts as another radiator in a pinch.
Getting a new radiator can't hurt, but it may or may not solve your cooling problem. I did some research on aluminum radiators and what I found is that the larger core tubes transfer heat (cool) better than smaller ones. Different manufacturers offer differing sizes. For example (this is not accurate, just off my head) you may see an ad for a 2 row radiator having 36 of the larger diameter tubes while another guy advertises a 2 row radiator having 48 of the smaller diameter tubes. You might think the 48 tubes are better and should cool more than 36 because there are more of them, but in fact, they may cool less because the 36 tubes have a larger diameter and throw off more heat, thus cool your engine better. Something to consider.
The factory had both a 3 row (2" upper & lower tank) and 4 row (2 7/8" upper & lower tank) radiator. Each radiator has different brackets. So if you were to move up from a 3 row to a 4 row radiator, you will have to install a new set of radiator brackets, rubber insulators, and for 1967, the upper radiator bracket that goes over the top of the radiator. These are all available aftermarket, so not a problem to get if you want to go with a factory type radiator. But whatever radiator you select, aluminum or factory type, keep in mind to know what size tanks you will get and if it will work with the available radiator brackets for an easy bolt in.