When you are removing the plastic plugs in the rear area mounting holes, be very careful. Their heads on the fender well side have a big wide slot. Be sure you use a screwdriver whose tip fits rather tightly in the slot. That plastic has become pretty brittle after all these years. I gave it a shot of PB blaster first. Even though the plug is plastic, I figured the potential for a little lubrication would not hut.Try turning the plug gently in and out a bit to get it loose and then back out slowly. If it breaks off in the threads of the body, your project just got a lot longer.
Gene