I went looking today for sprockets and chain...
Is 3000 rpm to fast for chain drive?
It is according to My suppliers.

I'm thinking a 525 o ring chain and two 29 tooth ( 6") sprockets.
The reduction is the belt part of the drive.
There will be about 25" center to center on the chain part and prop.

If I could find a "supplier " I would look at something like a serpentine belt .
HUMMMM ?
If you use chain what would you use?