if it's heating up at idle I look at airflow through the radiator first. I've had twin Spals that wouldn't keep an engine as cool as I wanted, but they didn't go that high. Make sure they have 13+ volts when running; an old stock wiring harness won't usually have full voltage up to the front of the car, and your voltage could be quite a bit lower than you think. Lower the voltage, slower the fans spin.
Also, how did you fill the system with water. An air pocket will also cause this and if you filled through the radiator and don't have a drilled thermostat that's another thought for your problem. Often there will be an air pocket up high at the thermostat area and it'll never open. I like to use a drilled thermostat (or drill 3-4 1/8" holes myself around the perimeter) to allow the water to bypass and push the air out. I also fill the block first through the thermostat area (remove it, fill until the block is full, re-install thermostat and upper hose) and then finish filling the radiator itself.
Very retarded timing will also cause them to heat up, but I assume that's been checked and is in the ballpark; if not, check it.
Jody
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