You can’t count the vac advance until it starts, so you’re only starting with 18 initial.
I had a rowdy 350 once. More cam than yours. 10 to 1 compression, trick flow heads.
I ran 22 initial, 12 from mechanical plus a limited 10 degrees from vac pot.
Used a limiter like this one in the link.
I can tell from the way yours starts that you’re close with timing.
Sounds good.
https://www.summitracing.com/parts/m...yABEgKeI_D_BwE