Spinner size is directly related to the aircraft not the engine. It sounds like a 3" is your ticket.

As far as spinner bolts / adapters that is directly related to the engine. Some engines have the prop bolt tapped for an 8/32 bolt or something.. some need a prop adapter. If the prop bolt is tapped put a bolt in there to see what it is tapped as and get one long enough for your spinner. Usually use black alloy bolts myself.