Unfortunately the flange on the output shaft is one I found locally and doesn't actually fit very well.
I brought it for a couple of quid as a 5/8 bore, and thought I'd been had when it had too bigger hole.
However I've had a better chance to have a measure up this afternoon and have now realised the propshaft is 5/8in, but the output shaft on the engine is 19/32in.
I could machine up two flanges of course, and either incorporate a small doughnut or something along the lines of your ebay link, but I'm really tempted to try some -10 Hydraulic hose which has a bore of 15.2mm or 5/8in with 4 clamps. It certainly looks and sounds like the easy/lazy way out.
I'll have a think about it, as I still need to source or machine up a stuffing box/shaft seal because I can't find one smaller than 1in at the moment.
If I have to sleeve the propshaft for that it will effect what I do with the coupling too.
All good fun, my trouble is having to go to work gets in the way.
RIBBED For extra pleasure.
Member of the ebay Blue RIB cover club.
Member of the Bombard 380 Aerotec club