questions on timing an engine

10* initial on a mild 360 might run, bet it would idle cleaner, more vacuum, snappier response at 15-16*

Find the total number where it doesn't ping. Depending on heads, open chambers around 35-36 is usually OK with decent fuel.

Lets call initial 15 and total 35, so the mechanical advance in the distributor needs to be 20*. Sounds like yours may have more than 30* in it. 42 total - 10 initial = 32 mechanical (if you actually got to the end of the advance curve at 3K rpm). I've seen mopar distributors not fully advanced until 4000 rpm sometimes. That's why you MUST rev the engine to the point where it stops advancing, not some predetermined number.

Think of building a house. you don't build the roof before having a foundation and framing. Initial is the foundation on a street car, everything builds upon it. So find the initial the ENGINE wants, not some number you choose.

Having a total number is next, to do the mechanical advance. Then you can adjust the curve, how fast it comes in, with springs. Finally you have vacuum advance if you want to run it.

Others have covered this and it seems to come up a lot around here.

I'll say this, time it however you want. If it's a straight race car, total timing works OK. I don't even do my race cars total timing method anymore. Some methods work better than others.