Arizona Model Crafters has an Albatross spinner that works, about $70 as best I can remember (almost as much as the whole M-1 kit). It's not truly scale, although it's the right diameter. The Bristol's spinner is spherical, the Albatros is parabolic, but the difference at that scale is small.

I also changed my Bristol somewhat. I enlarged the horizontal tail to make it closer to scale, and stick built it instead of using the balsa slabs that come in the kit. It probably saved a couple of ounces in the rear.

What is the diameter of the 90R3? I bet that would be a great powerplant for the M-1D, of which there was only one built. It had a 3-cyl Franklin radial.