FWIW, when I was looking at the Dave Brown adapters I saw some fine print on their web site that said four-stroke installations should use the prop nut that came with the engine and then the spinner adapter nut (making it the lock nut).

I bought one of the Higley light lock nuts and I think that would work fine in place of the washer and prop nut leaving ample room for the lock nut/adapter. The light lock nut is about the same diameter as a prop washer and the corners are beveled such that the "footprint" on the prop hub is a disc.

I have a TruTurn spinner on the way that is the Wide Blade version, it is supposed to be able to take an APC 14x6 without additional cutting but we'll see when it gets here...

Mark