I don't know exactly how they do it, but it looks like the nuts are conical. Of course, even though they exist they are nowhere to be found in stock. It will take till at least the end of August...or later to get them.
It would be pretty straightforward to use a spacer, but then I need to figure out how to source and install the longer studs. There's enough room to remove the stock length one's, but there isn't enough room to fit the longer one's. I've been looking through old posts about drilling the back plate on drum setups, but mine is a 280ZX disc conversion and I don't know if it will work the same.
I'll have to look again when I get home, but I recall some substantial metal in the way. The caliper brackets are 4 lug, so the stub axles must have been removed to install them.