This latest project won't get any prizes from the machinists, but as a "proof of concept" I think it may have some merit. At least it was a way to kill an afternoon without going out into the big old infectious world.
I have several old Manfrotto tripods, and though my main one has a Kirk ballhead on it, I also have a couple of very nice old 3-way heads that use the Manfrotto hex plates, and I've always kind of liked 3-way heads for landscapes and macros. The 3047 is very nice, and the 3039, with adjustable drag, is able to handle even very heavy components.
Although they're bulky and hard to store, I always liked the Manfrotto hex plates because they are easy to make. They are thin and flat, and they allow a protruding bolt at the bottom, no recess required. The problem is that if you use lens feet as well as a camera, the hex plates don't go 90 degrees around, so if you just put an A/S clamp on a hex plate, you have to remount it if you occasionally use a foot that's rotated.
I have an older Bogen head with a screw clamp, and it occurred to me to try making a round plate. That worked, so then I wondered if the quick-release Manfrotto heads can also use a round plate if the size is just right. Sure enough, though you have to sock it down a bit to keep it from rotating, you can use a round plate, and this allows you to turn it any way you want.
So here, anyway, is the quick and dirty version. The A/S clamp was milled out of a hunk of aluminum and should have its seating surfaces neatened up, but it clamps nice and tight. It's a bit thicker than usual, because otherwise you need a spacer to keep the clamping screw from interfering with the plate. The circular pad holds reasonably tight despite very small contact area with the head, and with a little tap on the quick release lever it's quite snug too.