I believe "Old Fart" is right on track, as the problem may not be the prop. Is the engine a Saito 82 with a plastic back-plate?

If so, the vibrations will settle down once you run it in, adjust the high and low mixtures, and adjust the valves. Also moving the muffler in towards the engine body will reduce the vibrations. If you have the plastic backplate, they allow the intake manifold to vibrate, wear the o-ring, and change the air-fuel mixture. Horizon sells a metal backplate for the engine, which I highly recommend.