[82 Silverado 4X]

Sounds like you are getting somewhere. I now have mine set at 8 degrees BTDC. I used Mike Irvins approach from his website (HEI TUNING SECRETS) to set my timing and only needed to make a few minor adjustments to it for my particular truck and the octane of fuel that I want to spend money on each week. Factory ignition timing settings are based on your engines factory internal components and the type of trans you have. Emmissions requirements also play a big part in where the factory chose to come up with their recomendation. Fuel quality and price for it in your area will be the deciding factor in how much advance you can run without pinging.

I started at 14 degrees on mine just to see if it would take it but it was way too much as I eventually found out. Try 10 degrees advance to start and see if it pings under full load. I moved mine in 2 degree increments until I found where it was just starting to ping when I was lugging the engine hard.
Good Luck