OK, here's my diagnosis. I have to check the gasket again, but it didn't look blown. There wasn't any coolant in the oil, and when this happened, the temperature was a bit higher than normal (about 95 C), but nowhere near overheating. So, I don't believe this is the case.
The O2 sensor light came on a little while ago, and I was going to replace it soon. So, I guess the sensor gave the computer a false signal causing a lean mixture, which in turn cause the extreme heat and that melted the piston. That also caused the higher coolant temperature.

Omegabenz,
I'm not running any NOS and the sparkplug is exactly in the middle. The pits on top aren't actually pits. They're bits of melted piston stuck to the top.

The cylinder wall actually looks pretty good considering what happened. It's just coated with aluminium at that spot, but I'm going to have the block bored to clean everything up.

Obviously, this ruined the rod, too. So, does anyone have any idea on where I can get one connecting rod?

I'm also going to check for leaks on the #1 intake runner, as that could have caused a lean condition on the cylinder. The other pistons are in fine shape and you can still see the cross hatch marks on all of the cylinder walls.

Thanks for all of your help, but the questions still remain:

1. Where can I find the dimensions I need to get custom pistons like compression height, deck height, diameter, etc? Does anyone have these?

2. What about cams? I've heard that stock cams are the best for most turbo applications because turbo cams just increase efficiency. Does anyone have the specs for the stock cams (lift, duration)?

3. Is there anything special I should know about building this engine?

Later,

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87 190E EVO II Turbo