Spark Plug Advice Needed

Lets get something clear for me. You say 16 initial and 34 all in by 3400. Then you say the vacuum can is on manifold vacuum. Now, did you set those timing figures with the vacuum hose disconnected? If not, that initial timing figure is very low, because "most" vacuum cans pull in about 20 degrees. Lastly, where is your vacuum can adjusted? You should "start" with it adjusted all the way clockwise, as that allows the maximum advance to be pulled in with the minimum vacuum setting. Then if you get spark knock, turn it counter clockwise until it stops. BUt if no spark knock all the way clockwise, then leave it be.