Has it been magnafluxed, balanced, and nitrided? Also check the radii at the edge of the rod and main journals. If they are less than 3/32" radius, then it's likely to eventually break at that point (smaller radius creates a stress riser). Are there some of those cranks flying? Yes. I know of at least one. If I was going to fly behind it, those are the 4 things I would insist be completed.
Your local auto machine shop can do an adequate magnaflux inspection, and if they have a reasonably knowledgeable machinist, they can balance it for you as well. Inspect the journals for the correct radius. Send it to an aviation crank shop to have the Nitriding performed (and the balance as well if your local auto machine shop isn't up to it). Then enjoy flying it. Nitriding may be optional as the early A65 - C-85 cranks were not nitrided. I think all of the C-90 and O-200 cranks were nitrided, but there may have been some early ones I'm not aware of that weren't. Someone on here will probably know the answer to that.
Seems to me the GPU crank also has one offset drive stud on the flange, so you may have to drill a prop specially for that crank if that's the case, but some of the aftermarket wood props are relatively inexpensive.
-Cub Builder
