Took me a while but I found the cam card, your intake valve, if you installed the camshaft straight up, closes at 57 degrees after BDC. I couldn't find a cam card for an 068 but it has an intake centerline of 113 degrees, and a duration of 288 degrees. Making a big assumption that the lobe is symmetrical, I calculated the 068 intake closes at 77 degrees after BDC. Even if your camshaft and the 068 camshaft were identical, the 262 intake centerline of 106 compared to the 068 intake centerline of 113 would make about half a point difference in dynamic compression ratio, the 262 being higher than the 068. With the added duration of the 068, 288 degrees, compared to the 262 degrees of the 262, the difference in dynamic compression between the two camshafts is even greater.
I don't know what camshaft you had in your engine before you had it rebuilt, but if the available fuel was marginal before, and the swap increased the dynamic compression ratio, it will be worse now. That's making another big assumption, that you had a camshaft with a later intake valve closing point than you do now.
You did say at 6 degrees spark advance initial and 22 total you eliminated most of the ping and the car ran well, why not leave it there, or a little less, and not worry what the numbers are? As long as it runs OK who cares what the timing light says?
