I am no authority on the making of prop adapters, but it looks like you need a two part adapter. One part fits the taper of the shaft and is held by the threaded end o the shaft and a nut. Then the second part is bolted to tapped holes in the first part. The second part is internally threaded either with one central bolt or four bolts spaced radially out from the )center. The prop is bolted to that (those) tapped hole(s). Some of the Chinese engines have this arrangement, and maybe one of those prop adapters might fit your engine? I think CRRC or CRCC engines had a problem with their 45cc engine adapters. Maybe search here for a thread on those engines for some pictures and things to avoid (like sharp corners with no stress relieving radii).

Good luck.

Sincerely, Richard