First, I think the 10x6 prop might be a bit small. After I soloed on my Alpha 40, with this same engine, I switched to an APC 11x6 prop, and it really makes the plane faster and a better climber.

As for the spinner, I just used a GP nylon spinner (2 1/4"?) with aluminum backplate, but I did not take off the stock flywheel. I do not know how this relates to your P-51, but it may make a difference depending on whether or not you leave the flywheel in place. I have heard that you should remove the flywheel when you stop using the three blade trainer prop, but I have left it on so far and no problems.

Good luck.