My 302 did not like the vacuum can advertised 15 degrees at 8 in hg.
Here's my setup, 15 degrees at crank / 10 degrees distributor (20 crank) total 35 degrees mechanical.
Test driving with vacuum my car would only stand 9 degrees at high speed cruise and idle decently.
I accomplished the vac setting by making my own vac canister stop.
My car would did exhibit a good idle at 30 (15 advance + 15 vac can) it does ok with 24 degrees and no ping at high speed cruise.