The spark is always before tdc as you said the flame needs time to burn.
When people refer to advancing the timing it means even more before tdc. So more time for flame to burn.
I can't recall where it was but there's some good info in the net relating to timing.
I understand you don't have access to a Dyno, so it's harder, but you should invest in some knick detection equipment, eg kmon or similar, because without it you are flirting with danger.