After knocking out most of my Spring Break Honey-Do list over the weekend I was able to make some progress today. I worked on it a little bit over the last week, mostly screwing things up: broke a bolt off in one of the side rails, cut my bottom armor too short, etc.
After ordering more 1/8" UHMW sheet, I re-cut the bottom armor using the table saw to get the major dimensions and the band saw to do the notch-outs. So far, so good, with the minor problem that it won't stay flat on its own (it came from McMaster-Carr bowed). I'm using washers along with the 6-32 machine screws to hold it on.
I also picked up some flat-head M2 screws and the appropriate countersink as part of that McMaster-Carr order. I replaced the pan-head motor-mount screws with countersunk flat head, giving me more clearance between the wheels and the frame. Similarly, I countersunk the 6-32 screws that hold the back piece of frame -- the pan-head versions were scraping the wheels. In retrospect I should have made the frame a little longer in the rear.
I angled off the front "mandibles" in preparation for adding the wedge. This was more work than I expected. It turns out our miter saw won't cut an 80-ish-degree angle (as measured from perpendicular to the stock). The closest it would come was 50-degrees, way too steep. So I had to free hand it on the jigsaw and clean up with a file. It looks pretty good.
Finally, I cut some home-made nutstrip out of 1/4"x1/4" Aluminum bar and used it to attach a 1-1/4" piece of 1/8" thick UHMW as a wheel guard on one side. The UHMW was ripped to width (from 1-1/2" stock) on the table saw.