It looks like the max advance really is +60.12. That's a huge range but that's what they use. Other DIS cars use all negative values.

The spark angle is also known as the reference angle. It's where the notch is in the crankshaft compared to TDC. Later engines put it at 75 degrees. Early engines put it at 60 deg. If your car never ran right without the advance then I'd think you had a mismatch between that number and the crank. But your car ran well until you worked on the head, right? No changes to the crank? So I don't think that's why all the extra advance is needed. You might be able to check the crank angle with an adjustable timing light. If you force timing to zero degrees then the light should show zero degrees. If it's off by 15 degrees retarded then you probably have a 60 degree notch crank. This article talks about crank differences. http://www.enginebuildermag.com/1999...the-gm-quad-4/