The water pump pulley and crank pulley is from a 73 318 non AC car and on my set up with the crank pulley it is 0.95 underdriven
Water pump pulley diameter
6 7/8"
I do not own a IR gun however I did put my hand on the rad and found no abnormal hot spots
I'd sure get one before you do anything. They are a very cheap, yet indispensable tool. It could verify your over heating, OR save you from doing anything unnecessary. .95 underdriven seems like a pretty small amount. But, I'm no expert.