those engines had a pressed on ground electrodes on the plug as well. lots of them get repaired because when the plugs are removed for replacement the pressed on ground comes off the plug and stays in the head. napa has a special tool for getting the electrode out (and there are lots of posts on the net about how to repair that problem), maybe they also have a kit for installing threads that were damaged. either way, always change the plugs on a cold engine or trouble will come looking for you.
grab a mirror or borrow/rent a snake inspection camera and take a look down the hole where the plugs go in (I hear harbour freight has an inexpensive camera, try to get the largest viewing screen you can find). you should be able to see if there are threads left in the head. also, did the ground electrode come along for the ride with the plug, or did it stay in the head? did it pull the threads out for the coil mounts? is the coil damaged? I have changed plugs on a few of these engines and never had a problem yet, but I have had lots of trouble with coils that worked fine when the vehicle came in for plugs, but misfired right after they were removed for plug access. not exactly cheap either. if you install new plugs always use anti sieze compound on the threads.
keep us posted and good luck