I have used a variety of radiators in 1200s. In the turbo motor, I used a three core from a mid 70s Olds Cutlass. I used a Pontiac Sunbird radiator in one. I am now using a three core from a 1987 Dodge Aries. I am in the USA and my uncle owns a scrap yard so I get to pick and choose and get things next to nothing. I am very lucky in that aspect. The three core radiator will not let the temp guage go up to the cold mark on a hot day if I do not have a thermostat installed.

To choose a radiator, pick one that will physically fit down into the space and it has to have the outlet on the left side. The inlet can be on either side as the thermostat housing can be turned to the opposite direction. The GM radiators are easiest to fit into the 1200. They sit into two rubber brackets that are placed into a small hole each. The top can be braced with a piece of sheet metal. On my first 1200, I cut out the front wall to fit the opening to the Olds radiator but on the other 1200s, I just left the original opening as it lets in sufficient cooling air. I eliminate the stock fan on the water pump on all cars anyway and use electric fans. They require less HP from the motor and less HP taken from the motor makes the car faster, quicker, more effecient and get better milage.

Keep it cool,
Mareo