Took multiple flips from pic to pic to get some kind of feel for the orientation of the panels. Think that the term "inner rocker" might be misleading here. What is missing from the Goodmark units is the entire outboard shoulder, incorporating the flat outer sill which would be attached to that three part, rocker panel "sandwich" all the way down and into the flat bottom of the pan itself. This mia element includes the outer shoulder against which the rear bracket for the front seat is plug welded as well as the hole through which the bolt for the lower seat belt bracket would go. On my 85 Monte Carlo, as created by the factory, that sill section actually had a flange that bent down to line up with the inner rocker panel and which then got plug welded to create the seam-joint. That flange pretty much ran the from the firewall to the B pillar. The other thing that I am looking at, and wondering about, is whether the Goodmark panels actually incorporate what appears to be half of the transmission tunnel. That being the case, to use one of these panels means you would have to include removing half the tunnel as part of removing the floor panel or its remains. With my panels, like the Sherman versions, the tunnel remained intact. That eliminated the need to set braces and reinforcing bars in place to keep the body aligned while disassembly and fitting occurred.
The version of the floor pans that I am working with right now is closer the Sherman version. The passenger side got replaced many years ago and I am finally dealing with the drivers side. What I found during deconstruction was that the body mount under the A pillar had completely died. I ended up cutting away everything except the firewall face of that mount and replaced it with one that I had had harvested from a Grand Am many years ago, just as a precaution. I had my yard cut both sides out for me jic. The rot was so bad that I had to rebuild the opening in the frame for the rubber biscuit as well. The reconstruction of the floor included salvaging what was useable of the old sill support that runs for most of the length of the pan, cutting away the rot and ruin, and replacing most of the lower curved sections with hand shaped panels . Along the way I also had to rehab the midway body mount that is also part of that subassembly. At this point I kind of wish that I had taken pictures but a lot of this was test and tweak so the frustration level pretty much matched the amount of tweaking that had to occur. Included in that prep work, because the replacement floor panel, unlike the factory original version, did not possess a mounting flange to attach it to the inner rocker panel, I also had to create an "ell" shaped flange as a substitute, plug weld it to the inner rocker panel, setting the plugs from the outside face, and then plug weld the sill to that ell to get my connection. Had the body been on a rotisserie, and the frame removed, it would have been simple to duplicate how the factory did it but this is a frame in place situation so creative engineering had to be employed.
The only other thing I would mention is that you ought to be aware about the possibility of rot in the transmission tunnel. Even though my S/S tunnel looked fairly sound, once I stripped the paint away a number weak areas revealed themselves. Oh yeah, don't expect the new panel to line up absolutely cleanly once you have cut away everything that is rust or junk. The replacement panels can and do vary in quality and fit and even if American made can offer fitment issues if the dies and presses are old. A last thought. This is not a weekend, out in the driveway, project. Just the act of removing the old metal means you will have to deal with the main line for the rear brakes, the cabling for the emergency, and the vent tube that runs from the gas tank to the charcoal canister as part of the emissions plumbing. Depending on how invasive your surgery has to be, all of these can and will get in the way. Not going to suggest how to marry the new to the old; personally I used MIG but that is because I have one. What you will find is that everything will take at least twice a long as you think it should and most of what is being installed will have to be "adjusted" to get that "just so" fit
