I just measured up my McCoy 049, thinking that whatever the mounting dimensions are, they'd round to some easy fraction of an inch.

I was wrong: it looks like the radial mounts are on an equilateral triangle, 0.837 inches (+/- 0.005 at least) on a side.  This doesn't seem to round out to anything sensible.

So -- anyone know for sure?  I'm really not good at measuring hole centers, as I find out whenever I finish drilling something up and go to try to bolt it onto something else.

Well, you're too late.  I've already drilled my test stand from measurements.  I can't say I nailed it, but everything fit on the first try (using a 3/32" bit instead of a #43 helped).