I have a 1957 235 with '848 head and the center looks just like Shipwright's link, with a small spring and spacer/shim on each side of the oil connector. The shim goes on the inside against the oiler like the pic.
However, the oil connector itself looks different. It does not return back to the head but is pinched off at the top so it will spray oil on top of the rocker assy.
