Which way is the little oil pump cover/ sump plate supposed to be installed on a 1960 C15? The documentation from BSA does not say but a couple of their diagrams suggest that the deep part goes toward the front. However, I have a rebuild article that shows it installed toward the rear.

Someone will give you the definate answer, but the oil would tend to be forced to the back by forward motion, so that sounds more likely.

Deep part at the back as that is where the scavenge tube is located