Good stuff here, I will add a couple points;
My 340 liked 15-18 BTDC, but had too much cam and compression(by design)so you should consider this the max. Even good ol' stocker 318s like 5-8 BTDC. If the timing chain is sloppy, even more.
I prefer to time street cars at max vacuum, then back off 2" of vacuum. Example-19" best=17" set.
Going with best vacuum tends to ping and make it hard to start hot. Just my observations over many years.