I found the exact size and shaft I needed for my aftermarket heater at Grainger. I don’t know about your Harrison. Worth a try. If all is good and you are just concerned about bad insulation on a couple of wires and can’t use shrink tubing, use “liquid tape”. Carefully brush on your coating. Google it.

Larry
Old man᠁Old truck᠁neither one goes very fast. All you need in life is TIME, PATIENCE and MONEY.
If you are missing one component, you'll need an abundance of the others two.