Hi Limeyrob, I agree with you except for the bit "This means the rocker oil feed may be less with a filter in the return". As the oil pump is positive displacement, then the filter has no effect on the oil volume returning (unless it is blocked). The ratio of oil flow to Tank vs Rockers depends solely on the relative resisitances to flow of the tank outlet hole size at the top of the tank inner steel tube vs. the rocker banjo orifice size. If they are still standard hole sizes, then the rockers will be getting the designed oil flow.
Col