I decided to make the gap filler plates from aluminum rather than using the fiberglass cutout's from the spinner. I began by copying the aft profile of the prop using a tool I bought at Sears that consists of a million sliding pins that you just press up against any profile or contour that you want to copy. I then traced the pattern from the tool to a piece of 0.063 aluminum sheet and made the cut on the bandsaw. The hard part was then bending the small gap filler plate to match not only the radius of the aft spinner bulkhead but also the forward slope of the spinner cone itself. I did this with a rubber mallet and a lot of iterations / adjustments of the part in the bench vice. I then pre-drilled the gap filler plate on the workbench, clamped the plate to the aft bulkhead and then used it as a guide to drill the flange of the bulkhead.
Gap filler plate fabricated from 0.063 aluminum
Gap filler plate with final bends and trimming complete