Mild 318 pinging

The timing numbers I already have up to 2000 rpm are as follows - 13* at 1200, 15* at 1400, 18* at 1600, 22* at 1800, and again 25* at 2000 with the initial set at 11* at 750 rpm. I also recorded 48* at 2000 with the vacuum advance connected. Granted, that is no load revving up in the driveway so it could be pulling in slightly less advance on the road. My math on cruise rpm at 55 comes out to 1932 rpm with my 2.76 gears and 26.4" tall rear tires. I could be reading the tach slightly off while driving as I didn't think that 68 rpm of slip sounded like very much. So if I'm reading the charts you provided correctly, I actually slowed down the lower end of the curve with my advance spring magic and really should re-install the long loop spring before going any farther. Thanks again for all of the info and help. It may be several days before I get a chance to plot the rest of the curve I have now and I'll re-verify the lower end as well. I'll also verify the reading of the in-car tach at several points.