engine trouble, oil pressure diving

Thanks for all the help! You guys have given me some direction and things to get started checking. Thank-you!

The car is a 4 speed and the oil pressure guage is mechanical (oil line to the gage).
Oil level is full/normal.
I pulled the valve cover on the passenger side where the ticking has gotten loud. Nothing visably wrong. However there is one rocker that can be pushed 1/2 inch with my fingers while the others that can be moved (some cannot move due to valve engagement) only go about 1/4 inch.
This seem suspicious.