The Stovebolt Site Forums The Shop Area Engine Shop Valve Cover Gasket Replacement

That's definitely a 216 head casting number. And the rocker oiler tube is copper. It looks like things may be plugged with crud or there just isn't enough oil getting up to the rocker shafts to get oil to the higher front rockers. It's essentially a gravity system with that overflow tube shown in the attached pic of yours. If the rockers are worn enough then the oil could run out around the rear rockers and never get to the front ones. An old timer trick is to pinch off the overflow tube to force more pressure to the rockers. But I would remove the rocker assemblies and clean them up and inspect. They may be too worn and ready to be replaced. R&R of the rocker assemblies isn't a hard thing and you're planning on adjusting the valves anyway. Reattaching the tube to the oiler assembly can be a little fiddly, but if you don't bend the tube coming up from the pushrod gallery, it should thread back in easily.