As long as it doesn't ping, the extra advance wont hurt a thing. since the timing is easily set and your reference marks are there, you can change it back to stock in about 3 minutes. I'd play with it, as its free extra power. Plus if your timing marks are off at all, you have no way to set it to stock in the first place.
I don't know exactly what my trucks set to, but the timing marks say its at 20 degress BTDC. and this is on 87 octane gasoline. I doubt it would run that well that high so I assume my marks are off a bit. And at 8 degrees like mine should be set to its a total dog.
When you test for spark knock, don't automatically romp on it to test for knock/pinging. as knocking/pinging is bad. on mine, I get up to about 40mph or so and press the gas as far as I can without it downshifting. doing this the trucks not so loud so I can hear the pinging better. then if that test goes well, floor it all the way and see what you hear. if you hear pinging, drive the truck EASY back to where ever you have to go to readjust the timing. I go up 4 degrees at a time to save time, and then when it pings I back off 2 until it quits.
On my truck, Having the advance set where it is as opposed to where the timing marks say to put it, I have to push my gas pedal about 1/4 less to do the same work it did before. It takes off faster on the primaries than it did before on the primaries and secondaries.
Play with it, if you feel uncomfortable with the adjustments, put it back to stock. you can always do that, and it will be perfectly ok.