[Bob Bidonde]

An abundance of oil needs to get into the dip tray to assure the connecting rod troughs become full. The oil return pipe takes excess oil pump volume and returns it directly to the tray. My guess is that Ford decided it was less complex and thus less expensive to eliminate the oil return pipe by putting drain holes into the bottom of the valve chamber.

However, as the bearing feed holes are also in the bottom of the valve chamber, the oil supply to the bearings becomes uncertain. So Ford went back to the oil return pipe which assures a good oil return without threatening the bearing's oil supply. The oil flow through the return pipe is regulated by the position of drain holes in the valve cover, and size of those holes.