Hey Grant, the Brison (exellent choice, BTW) is a single bolt hub, also.
But here's my 2cents.
Buying or not buying a engine based on how the prop mounts is just plain wrong.
Please reconsider.
If that's your primary consideration when purchasing your engine regardless of preformance, customer service, and reliability, that's your choice, but I hope you adopt a few more critieria.
I have a engine that use a single bolt, and a DA that uses 4.

I love both my engines and wouldn't get rid of either one, but the way the prop mounts hasn't even been remotely important.