Usually too much advance timing and or lean fuel mixture but low octane rating is another thing that can cause it. Detonation is actually pre-ignition, the fuel/air mixture ignites too soon prior to the piston being at TDC and the flame path isn't uniform. Carbon deposits can also get hot and cause detonation. What it does to the piston is in effect like you took a sledge hammer and hit the top of the piston, that in turn hammers on the rod bearings and drives the oil film out of the bearings. The end result is what happened to your bottom end.

Lack of fuel, too much timing, bad fuel, excessive heat, or not enough octane for compression ratio

Keep in mind that reversion can produce detonation too. The water cannot compress, which can raise the CR through the roof. Notice that the carbon is blasted away from the quench area. You see a perfect outline of the chamber on the top of the pistons. The water cannot compress in this area, and essentially blasts all the carbon off.

I'd think if reversion was the culprit there'd be at least a minimal amount of rust on the cylinder walls. My thinking is the carbon was burned off. I don't see any evidence of water being present in the combustion chambers.

I'm with payup on this. Those pistons don't look steam-cleaned to me. That looks like the carbon was detonated off. Steam cleaned pistons are clean as a whistle.

Detonation can also occur at startup, which might explain your starter problems. Detonation can cause the engine to kick back, taking out the starter. Take a look at your distributor (if applicable) and ensure the advance weights aren't frozen. Also check your cam timing and make sure the timing set didn't skip a tooth (although they usually skip in the retard direction, which wouldn't cause this issue).

As a confirmation, look at the insulators on the spark plugs. The carbon that was blasted off the piston crowns tends to deposit on the ceramic, and looks like pepper.

those pistons aren't steamed cleaned.those pistons hit the head after the bearings went totally away.now why did they do it.look at the bottoms of the piston and upper bearings.take pics and post.but you did have the head gasket gone for a little bit.notice the loss of the fire ring.

There are no upper bearings left to take pics of. Head gaskets look like new.

between the cylinders is burned,,gaskets weren't sealing.well look at the bottom of the pistons,,do they have burn oil on the bottom?

I don't think the pistons hit the head, especially with the rods bent. The reason the carbon is gone from the perimeter of the piston is because that's where the least material is because of the proximity of the ring land and that's what gets the hottest. Usually you'll see the ring land try and lift because the ring is trying to stick to the cylinder wall and the ring land is weak from the heat and can't hold the ring in place.