Looking at the shop manual, it appears that the breather cover and spacer can be reversed, but the seal under the spacer wouldn't match the casting in the valley. There are two cast walls to the left, and one to the right, from what I can tell. The drawings aren't the best, but it seems to show a large cast tube on the left end of the breather cover, which, I assume, is for the breather tube. also, of only the cover is reversed, and not the spacer, it would totally mess up the breather function.
EDIT: I just looked at the first page of the cylinder heads section, and the cover looks really different. As does the drawing on the first page of the crankcase section. Looking again at the drawing that shows the cover and spacer exploded, I see that what looks like a large tube is just a shape in the casting, and the (smaller) tube is on the right aft side of the cover. It appears that there is an oil pipe for delivering oil through a fitting in the cover to the top of the cylinders, so that can't be reversed.