You'll want to use a dialback timing light to make sure your total doesn't go over 35-36 in the mechanical advance (vacuum advance unhooked). Most small block distributors have 15R or 17R plates (30 & 34 degrees of timing in the distributor respectively)...so you'll need to weld up the slots to make them shorter.
I made my 15R plate into a 10R plate. Then i set my timing to 15 deg BTDC. I now have 35 total and my engine is happy.
I'd bet around 10-12 on a stock engine, since my engine is modified.