Oil Flow regarding Head

[Old School]

Let me catch you up to my scenario before I ask my question. I recently took the head off my GZ to find that the cam shaft was trashed, bearings shot. The head looked like it had not seen oil or any other lubricant in years. I don't want to put a new head on it and have the same problem with oil flow. I understand there is an oil pump in these engines. Has anyone ever seen this due to a blockage preventing oil from reaching the head or is this a general symptom of a bad oil pump?

[Water Warrior 2]

Can't recall hearing this before. I think the previous owner may have run the bike real low on oil without realizing it. If that was the case what oil was left would have been working hard and might have lost it's ability to flow efficiently with added heat. Just guessing though.