I'm not understandining if you lack oil to the lifters or the entire engine. I would ask your mechanic to disconect the fitting in the block that goes to your oil pressure gage, spin the pump with a drill and see if anything comes out. If not, I'd say you have problems that would at least require droping the oil pan.
If the problem is only that your lifters are not getting oil pull off the side cover (lifter cover)and you will see a steel brake line type tube that runs from your rear cam bearing to the middle of the block. From there oil goes through the head up to the rocker assy. I would disconnect the tube at the cam bearing and run a wire into the fitting to clean out, and try the pump again. You may find the tube is plugged. Mine was so bad that I just replaced it.
