I spotted a 3x2.5 3-blade Cox prop at the LHS today, so I snagged it since I never had one before. It's a homely little thing with bell bottom blades. I think it is actually stiffer than the 1/2A black props, relatively speaking. I could be all wrong, but I have a hard time believing it is a terribly efficient prop.
But what I found encouraging was that the hub on this thing is very similar in size to the hub on the fg combat prop I trimmed. Weight is similar too. It might work well.