newly built 416 stroker timing adjustments

Sounds like you have 18 deg initial.

But what is your total? Rev until all you mechanical advance is in (2500?). Then note what degrees that is. I'm guessing 30-32 deg.

Since it's new I'd go conservative with total timing around 28-30. Then after 200 or so miles up the total until it pings and back off a couple.

I don't know what compression and cam you have. Mine is 9.7:1 measured, CC'd with a comp 274-S cam, I have decent quench. I have to deal with California spec 91 octane out here. My timing is 32 deg total. 34 deg will ping.