Before you do anything, check the timing, back flush the coolant system and take your radiator and have it hot tanked and rodded out if necessary before you do anything else. I'm not sure that an electric "pusher" fan will do much as you currently should have a direct drive fan on your car. However if your wagon is idling to low, that could be a factor when stopped.
When the car is running hot, have you checked the temperature with a heat sensing gun? If you put the car in neutral and increase the engine RPM does the temperature start to go down?
My recommendation would be to have a 3 core narrow fin radiator fitted to your tanks and add a factory two piece metal shroud, a 7 blade fan and a clutch fan. I would also back flush the cooling system extensively with a chemical agent designed to clean cooling systems. Keep in mind that the green coolant that we use in our older cars can turn acidic after 2 years and eat away at an aluminum radiator. Using modern long life coolant isn't an option as it will eat away at your heater core causing it to leak.
Post a wanted ad for a two piece 22" fan shroud for a C Body. The B Body reproduction shrouds may work.
Another alternative would be to install a 26" radiator but your core support opening is for a 22" radiator so part of a 26" radiator would be behind the core support and require you to drill a few holes. This would give you some additional cooling capacity.
