[L78steve]

The taper ground into the lobes is for lifter spin. I may have a secondary effect of pushing the cam back I don't know.
The reason I believe this is that every cam (flat tappet) Ive installed with a button never made any contact with the cover after disassembly many runs later. The clearance set was the gasket thickness. So I have assumed the cam was held rearward by pump load.
Roller is another issue the plate is needed for insurance that the cam will not walk.
Don't mean to be a PITA just info gathering.
Also i have seen blocks run with high pressure pumps worn from the cam gear contact surface.
Pumps put one hell of a load on the cam gear. You can feel it when pre-lubing. Also oil pumps are loaded weather spinning up or down in RPM.