360 timing advance problems

Your mild 360, will like idle timing as high as 25 or more degrees.
The Vcan is not likely to pull more than ~14/16 at the most and only with a high intake vacuum. But suppose it does at whatever idle vacuum you have.
Suppose you set the mechanical timing to 10*. Hooked to Full manifold Vacuum, that would be a total of say 25* which is NOT too much to idle on. But if you set your idle-timing to 20*, now you could be pushing 35*, and there is a very good chance that your mild 360 would complain about that as you tip the throttle in.

Here's the thing; when cruising the hiway, your mild 360 might like 56* of cruise timing. With just 15 in the Vcan you would need 41* in the mechanical plus idle. You could do it with say 25 in the mechanical and 16 on the idle. But your mild open-chamber iron-headed "monster" is sure to detonate itself to pieces when you nail the gas.

All numbers are hypothetical.
And the other thing is this;
Most or a lot of guys will just adjust the distributor to hit 36* at 3600 rpm or thereabouts, and let the idle-timing be whatever it will be, as long as the engine has enough power to idle on whatever it thus gets. By the time the engine ramps up to stall rpm, the Vacuum advance should have dropped out, and the total power-timing could be ~24*, or perhaps a lil more. While maybe not ideal, it ain't that shabby for a mild 360; and at least the pistons won't rattle their skirts off.
Could you do better? Probably.
Should you do better? If you are careful and take your time sneaking up on it, sure. But again; 3* not enough power-timing might be 7hp over the nose. But if to get that 3*, the engine detonates below say 3400, then that would be a bad idea; DON"T go there. Your azz-dyno will never notice 7hp in your 360 on the street.

Happy HotRodding