Plastic is the way to go.I drove about thirty demos with Pintos,with out fans, before starting to run a fan.If your radiator is getting that close,the pump is going to put a hole in your radiator anyway.When you run a fan,the motor is a least cool when you do loose your coolant.I always weld a 1/2" washer inside my thermostat housing to replace the thermostat.A 9/16" opening is perfect.(measure the opening on washer)