Hi Mike
Like you already know you have a couple of ways to tackle this issue, It sounds like you would rather go with a single bolt prop adapter, but if all else fails some bushings will also do the trick. But a 3.5 MM bolt is not the strongest item there is and a backfire or loose bolts or as you already said over sized holes could lead to a shearing problem.
I can make a single bolt set up I am sure W/O to much problem especially if you have the new prop hub, but I would need to have a look at things to make sure.Of course a drill guide with the proper sized holes in it could also be made so there are several ways of doing this to come up with a good safe set up that will last for years. Can you post some pics so I can see what it is were working with?
Richard.