I went with this cylinder which, while not designed for this specific application is pretty sick and doesn't require any stud spacing or stroke changes.
The only issue was that even the VERY large transfers on the kit are tiny compared to the ones in the case. I actually got pretty good at this after matching the kit to the massive transfers on my Vespino.
Basically the goal was to create a shallow trough to help pull charge into the transfers, not really going whole hog to create a cavern. Small round carbide to set the perimeter and end depth, than I chased that back into the transfers with a teardrop and spearpoint carbides, finished off with handfiles.