i just went thru the same issues with the prop flange on the new engine. luckily i had access to a newer warp hub and flange inserts. the problem was with the spinner back plate. chucked the plate in a lath and cut out the center flange hole to the correct size . i had reamed the holes in the plate for the flange inserts nuts but the plate wouldn't fit. seems all the holes had to be stretched a little to get the plate to fit. enlarged center hole was pretty much dead nuts center so that wasn't the issue. all the holes had to be stretched in the same direction so it had to be some difference between the flanges. i did find the paper work that tells about the flange changes and has the engine s/n when they changed.
at least now i have a useless old style warp hub that will probably go away when i decide what i happening to the old engine.
good luck
chuck