Hello, you have your work cut out for you! I'm the guy that is rebuilding the 87YJ with his son. There is a square lock plate sealed between the underside of the body and the floor of the jeep. There located in reinforcing "channels" and can be accessed by cutting a "t" directly above the bolt, then peel the metal back enough to grind the tabs welded on the lock plate to hold it in place. Just need a nut and washer for install. Then we pushed the metal back in place and used a hardening putty from por 15 to seel it back up. The 2 back mounts spun the plates for us as well and for those we had to cut from underneath the jeep, just cut 2 corners of where you can see were the bolt goes up through. Hope this helps!