Low oil volume

The 273 in my Dart appears to have been rebuilt at some point in time since it currently has hydraulic lifters. The rocker shafts have shims under them, so I am guessing there has been some block/head work.

While adjusting the rockers, I found there seems to be very little oil getting to the rockers. With the engine running, there is barely any oil making it out the rocker holes. I do see some running down the shaft stands.

I am afraid the low volume ( but 55 psi ) could indicate the cam bearings not properly installed.

Or maybe I am over-thinking it and removing the shims, and changing to proper length pushrods, will cure the problem.

Any thoughts or insights??? I really don't want to do a motor swap or rebuild, but will do what is necessary.

My knowledgeon small blocks is limited, but currently on a steep learning curve.