I really want to just wing it and pull it out but that has the risk of immobilizing me for a long time, and I also want to just skip it and give er hell but that has its own risks as well.
A catastrophic failure is usually not cheaper then a planned repair. Take the time to fix it now instead of when the engine blows up.
TimeSert's are the way to go. A dab of red loctite and they are there for life and stronger then the original threads. Helicoils are more for two mating pieces/flanges where it doesn't get unscrewed a lot. Like you would helicoil a thread in the back of the block that the tranny bolts to.
You will need to call a real mechanic or a machine shop to see if they have the tools to do an on-vehicle spark plug repair. Since I doubt they have a Lincoln LS listed in their cheat sheet you can try telling them it's an Autolite 3924 Plug. If that still means nothing then you will want to tell them it's an M14x1.25x19 gasket plug. If they still seem confused go somewhere else. This is a pretty common plug style with imports so I am sure a machine shop or real mechanic somewhere has the tools and experience to get it done.
The actual TimeSert's themselves are only $5 or less, so you are looking mostly at his labor to install it. Assuming his tools can get in there, it's a half hour or so to install one. If he can't get his tools in there, then you will more then likely have to pull the valve cover off so he can tap it. Might even be able to talk him into driving by to do it.