The unit engines fitted studs without an adapter. AFAIK all alternator primary cases need the adapter. I find that new "pattern" adapters are often to tight to the stator encapsulation, had one last week from my stash, but an original I had was fine. These pattern adapters are cast, with just the mounting bits machined, so you need to take a dremel(or file) to them to clear the encapsutation . I'd be very careful about removing any encapsulation, just clean up any mould flashing.