I finished up these parts for the weekend, and boy, am I glad to be done!
This one feature that I'd been dreading to do ever since I saw it I was able to make with a 0.0002" (two tenths) tolerance!
I briefly mentioned it in my previous post, when the L-shaped part is put with the elbow stick pointing up, there's a small pocket relief at the very bottom. Normally this wouldn't be a problem, and you could take several stepdowns while finishing that side vertical face. However, the problem is that the vertical wall isn't actually vertical and comes in like a dovetail. The angle is very slight, only 0.88deg, so it isn't easy to see by the naked eye, but still there.
I was able to mill this feature with a custom ground back 3/8" endmill turned into a slot mill. Using this tool, I took several light passes to clean up the bottom of the pocket; then, with the tool's reduced neck, I was able to get under the angled piece and clear out the pocket.
It wasn't as scary to run as I initially thought. My expectations were that the undercut would have a very rough finish, and the corner wouldn't blend very well with the angled wall. However, I was pleasantly surprised by the outcome. I took several tenth staircase steps along that wall to blend the tool's square shape in better with the remaining surface. The tool didn't squeal, and everything ran very smoothly!
I am thrilled to see these parts finished, a lot of headaches and mistakes, but all learning, that's what I can console myself with. The overall tolerance on these pieces is within 0.0008," which I'm extremely pleased with!