Thats alot of prop. I was thinking you would be using something like a 11X7.5 or 11X8 to fly with. I am not an experienced 60 size engine man so I might be off on that. I would tune it with a prop that is atleast 1" diameter less that what ypu will fly with to simulate an unloaded condition.
ckecking in the xtreme threads might be a good idea.