Compression/octane

Thanks rumble, that looked like detonation on that piston, but rest are fine, randomly checked bearing; even on that rod, no signs on upper shell. Maybe it was the piston's time? (used engine bought in 1978, never took it apart).
Another ?; been welding, so haven't hooked up the mallory hyfire 7 yet, but that engine will not idle under 18 degrees initial. Set it there, then changed dist, mech only for total 36. Sound ok for the octane?