the stock rocker shafts have a notch on one end of them... That notch always goes DOWN & To he left, no matter what side you are working on, Drivers side the notch should be down & toward the front of the car, on the pass side it should be down & toward the rear of the car. So make sure they are not on upside down or backwards etc.

If rockers shafts are on correctly then it gets more complicated, has the engine ever been apart and how was it maintained?????

Basically in an LA Chrysler the oil for the rockers comes up an oil feed passage in the block that gets fed off of the #2-4 cam bearings...... The drivers side gets fed off of the #2 cam bearing and since you have 67k its possible that the bearing has spun blocking off the oil feed( not probable with 67K but anything can happen) or if any large chunks of debris gets into the oil passage in the block it can clog it easily as well.....

i would hook up an oil pressure gauge and see what you have first and then go from there