What do the cam lobes that mate with the pitted lifters look like? If you choose to replace only the damaged lifters, you'll need to do the same sort of break-in run that a new cam and lifter assembly gets- - - -20-30 minutes at 2,000 RPM before idling the engine to allow a new contact pattern to develop between the lobes and the lifters, and hope the cam lobe doesn't go away. How about the contour of the bottoms of the other lifters? The bottom should be slightly convex, so a straightedge rolls over it from side to side, not flat or concave. If the lifters are flat or concave, the cam is worn out also.
Jerry
