Why not just lock it out at 35*? My 493 loved that set up, and it spends 99% of it's time on the street. At 10.2 to 1 compression, the cranking compression is 200 psi. It never kicked the starter back.
I eventually changed the MSD Pro-billet out for a Progressive programmable unit to get adjustable vacuum advance. Now my timing cranks at 10*, goes to 35* at idle and 42* at cruise with full vacuum.
