This is a tough question because of your high compression pistons. I hope someone else jumps in with experiance and comments.
With the jumper the timing starts at about 26? BTC. Without the jumper it starts around 31? BTC.
It seems to me that with your pistons, you might want to try moving your timing in the other direction.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC