Now, given that this is a Duratech, good luck getting the head(s) off with the motor still in. It CAN be done but what a PITA.
Second, these plugs are tapered seat. Meaning that the threads are actually tapered to be narrower on the piston side of the threads than the "head" side. If you used a straight thread tap to clean the threads up, you'll need to drill and heli-coil that cylinder. One trick to tapping is to put TONS of grease on your tap before running it through to keep the shavings on the tap instead of falling into the cylinder.
Good luck with what ever route you decide to take. Neither is all that much fun. Personally I'd choose the second option.
