To determine whether the crank was scrap or not, I assembled it in the block together with a rod and piston, and added some 'engineer's blue' to the journal, then span the crank around a few times. With the rod cap removed it was apparent that the mark on the journal, although reasonably deep, didn't bridge the edge of the bearing surface which would have caused a loss of oil pressure. Based on this I decided that the crank should be fit for use. Time will tell!