At this point it looks like Poser11 works fine with the Reality python3 reality scripts - so I suspect that either Poser 11 did have some support for Python3 beyond Python2, or that the specific Python modifications to make these run in Python3 were backward compatible with Python2.

So I decided to install the Poser 12 free trial to test these mods. It appears to me that Snarlygribbly's avfix.pyc may now be the next stumbling block. Because it's compiled I can't try to convert it to Python3. I tried hacking the header version number in a hex editor to no avail :(