Yes, I advanced mine 4° but ONLY after degreeing the cam to see if that was the right thing to do. The stock cams vary much more than aftermarket cams so you need to degree it to see what you really have.
You have to have the right tools to degree a cam - Crane's website has a good tutorial on how to degree a cam. You don't need to buy their kit, a good degree wheel from Summit (~$25) and a good dial indicator is enough to get the job done.
This degreeing a cam business is something that still confuses me a bit.
I have a B303 in my 'vert and it's installed stright up. From what I've learned over the years, it is ground with 4 degrees advance (I think). Would there be an advantage to degreeing it +/- 2 or 4 degrees? And what effect would advancing (+) or retarding (-) it make?
If it has 4 already ground in, taking it further probably won't have a huge affect. Generally, advancing moves power band down some and retarding it moves it up - BUT that is totally dependent on actual valve events. My advanced cam moved power up.
OK...so... the B303 is ground with the intake opening 5 BTC and the exhaust closing at 5 BTC. That makes it retarded as it's ground and if it was advanced 5 degrees it would be opneing the intake at TDC, correct? And that would pull the power band down in the rpm range?