that is really light on oil, looks like there is some as the valve springs have a bit of a shine to them.
what I would do is
1) shut off the engine and remove the rocker shaft and pushrods.
2) without the rocker shaft in place, have someone crank the engine while you watch the #6 end rocker stand, you should get a decent pulse of oil out of the that rocker shaft bolt hole. There is a through hole at the rear cam journal, not a groove like the hydraulic slants, so you will get a pulse of oil with every 180 rotation of the cam and the cam spins at 1/2 crankshaft speed. If you do not get a strong pulse of oil, post back here at FABO with a video of what you do get.
3) remove the rockers from the shaft, soak the rockers in a solvent over night or longer. Can also scrub with Dawn dish soap and hot water.
4) clean the exterior of the rockers and probe the internal oil passages on each rocker with a thin - stiff wire. You can also use aerosol carb cleaner to run a blast of cleaner through each passage, wear safety glasses, do not get that stuff in your eyes.
5) Clean out the inside of the rocker shaft, you will need to remove the pressed in cup plug at each end. Soak in solvent, use hot water and dawn dish soap and a bottle brush. A competent machine shop will have replacement cup plugs as will Summit. Use a ring of red loctite on each when re installing.
6) Re assemble and re install and see if you get more top side oiling.
Note on the re install it is important that the oil holes in the rocker shaft point the correct direction, they should point to the valve spring side. There may also be a small flat on one end of the rocker shaft. That flat needs to be on the front - top side. That will get the oiling holes correct as mentioned above.
