I think gear reducers are allowed for the advanced class.

Timing the ports for slower operation would be helpful when you compare it to what a nomal JET engine is timed for. The Jet engines are for small props and you want a bigger one. But of course you don't want to go too far with that. I would think the timing of the Fox engines would be about right, but with more exhaust duration to allow more power increase when using a tuned pipe.