I grenaded my slant 6

I was heading down the freeway, breaking in some new 3.55 gears and the oil pressure went to 0 and there was a clunking noise. So I pulled over. When I tore the engine down the main bearings were all destroyed and the crank needed a .030 grind to make it usable again.

So what caused the failure? The machinest said lack of bearing surface area.