Now remember: I don't know what I'm doing, but I'm doing it!!! Distance between the side channels is 45 1/8". I cut off leaving a little extra. This turned into a lot of fit, no, grind more, fit, no again, try grinding more, fit now, no, more grinding. Finally it settled in very nicely. The original piece had three tabs bent out on each end as it was spot welded. Since I was going to MIG weld it, I did not need the tabs. I prepainted a majority of the piece top and bottom masking the top of the lips. I'll repaint everything again once complete. So there are those funny quarter panel lower braces that sandwich in between the mount and the channel. I drilled out the channel and two select locations and plug welded it. You can see it to the left of the bolt. Here's the underside of the same condition. The original welds were a pain to undo. I may hit the ends where it hits the side channel and weld from underneath. We'll see. So I still need to touch up a few plug welds. I also need to measure for the top plate that covers everything. That will plug welded in a similar manner. For the body mount bolts, they will not extend any higher than what you see. The original had this nice recess that I could not create big enough for a 1/2" bolt and a washer (although some tests came out pretty good!). I will make an 1 1/4" hole on top to access the bolt (and use a rubber hole plug).