Tim,
there was a change in 1950 to the 235 US engine and a similar 216 engine in Canada. Although it was still a low pressure version, the feed to the rocker arm was taken off the rear cam shaft bearing supply. Here is the explanation in the 1950/51 manual.
Oil Supply to the Rocker Arm Have a look at Figure 5 and the paragraph directly about the figure. You see the oil distributor still exists but it does not feed the rocker arm.
The engine being discussed here is the 1953 235 which had evolved a little further and used the more modern head but still had a low pressure oiling system.
