Update: done, mostly.
The drilling and grinding was most of the time spent. A milling machine would've sped things up quite a bit.
Also working out how to re-shape the bolt ends to shim them to the body so they're level. This shouldn't be to hard to do with a piece of scrap and maybe a hammer.
The tricky part was cutting the tubing to the proper height, even on both sides, so the ends will jut out at the same angle and height. On the second one I cut too much near the back.
Here it is tacked for final fitting.
And welded and filled...
Installed. Still need to add some material on the low outside ends to make them come level. But I do think this will work.