Unplug the vacuum canister and set the total advance to about 35 BTDC. To do that, rev the engine up gradually until the timing stops changing then set it to 35. Let the engine drop back to an idle and note the initial timing. That will likely be around 12-15 degrees depending on how the distributor is set up.

Usually the mechanical advance should be all in by around 3000 rpm but that varies slightly depending on engine combo and fuel quality.

As you've found out, the H cam works quite well even in the "little" 350 as long as you have enough stall speed!