[flatford8]

I’ve never seen a head bolt heater. But I never ran a Flathead in my younger days. I’ve seen dipstick heaters and I used a few that went in the lower rad hose.
I remember my father putting a light bulb on top of the motor and draping a blanket over the fenders to try to keep the motor warm. Tried anything to be able to get to work in the morning…..Mark