Ok, if anyone needs help, here is what I wound up doing.
Seems like it will work well. I plan to hold onto the bases while I spray, then set them on the oven tray and slide the tray into the oven. Lower doesn't fit top to bottom unless I take out the rack and put the tray right on the crumb pan (but fits easy then).
Oven is a Black and Decker
TO3250XSB "Internal dimensions are approximately 16.5”x12.5”x9.5”. "
Wide enough to fit the 15" handguard I plan to get (will figure out how to suspend that when I get it....)
For the lower I got a 1/4"-28 (fine thread) screw and put it through a piece of bent sheetmetal. Could probably use a piece of wood and run screw up through it (try to match angle of grip so it will be level). I used two lock nuts, one to lock the receiver so it won't spin and the other to lock the screw to the sheet metal (this way I can turn screw into receiver instead of spinning receiver on a fixed screw and then lock it in for rotation). Was back heavy (would tip over toward screw) so I put a sheet metal screw in to act as a "kickstand".
The upper fits perfectly on a 1" wooden dowel. I think the dowel will seal enough that it will "mask" the inside of the receiver where the BCG slides. So I just made a wooden support (paper burns at 451F, so I think I'll be safe curing at 300).
Pic of the lower mount won't load for some reason. You can see it behind the upper mount on the photo in the oven, pretty simple.
Got an Imgur account, hopefully pics will show...