Hello there,
Working on the assumption that you're using the propshaft that came with the kit, you'll find it is M5.
I can recommend George Sitek as a reliable supplier of good quality props and he does an excellent Kort prop.
His web address is
www.gsitek-props.co.uk , I've no connection with the firm other than as a satisfied customer.
I'd say your two part epoxy will probably be fine, but I've not heard of "Fiber Poxy" before. If it's similar to Araldite, then
go for it. Good luck with your build.