Cast iron 390/428 heads with hardened valve seats and bronze guide inserts. 72cc cardioid chambers, but likely with 10 thou removed during resurfacing.
Back during testing, I could tell the engine was fighting me at 28 intial, but not at 24, so I sort of thought 20 was safe. I'm actually searching for the lowest initial timing that still gives me a good idle and low rpm operation.
Never had any problems cranking engine. With idle set at 20 degrees, the dist springs are already working a bit. Cranking is more likely about 15 degrees.
It did seem to me that the crackle went away about 1/2 way through rpm range. Sort of ends when the advance stops advancing. Could have been my imagination, so that's another thing to check next test drive.