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Back off one or two inches as read on the vacuum gauge. When you do your test driving though for the next while, always carry a half inch wrench in case you need to back off more. If you have it too advanced, your engine could ping under heavy load. No bueno.
Hard to say about the valves. You should be fine though as engines don't run well at all if your valves aren't sealing.
I was able to get about 3/4 to 1 more inches more vacuum. May have been a little better running. No backfires. Engine does not diesel. Starts easily as well (pretty much always has).
Lots of clatter, but it was clattering a lot before as well. Perhaps I could not hear the pinging under the valve clatter.