Mhh cause I donīt know too much about these I canīt really tell if those are regular HB size or the soapbar type. If they are the later I am afraid you are out of luck as BKP does not manufacture 8 string soapbar HBs, they only recently introduced the 7 string version.
If those are regular 8 string HBs in their size but they are just direct mounted that is easier. I think I recall you would have to file down the mounting aids on the sides of the HBs then, but that it is possible.
Canīt think of a way rings would help there with those dimensions.
This is what I recall, so take that with a teaspoon of salt at least. There are people on here who can help you much more.