[Bruce of MN]

I didn't know that a spark plug had female threads. After breaking out the ceramic, I used a load rated forged eyebolt and nut and centered it with JB Weld, then ground the nut corners to clear the spark plug threads. Welding works, too.

I don't think a heat gun would make much difference at the joint. Maybe a propane torch at the studs, with your favorite penetrating oil.

A search here for Head Removal should give you a lot of tips.