I have a 1984 jeep with 4 cylinder 150 ci engine, I know it is a different engine than yours.
but, I had a new long block installed, after about 5k miles one of the valves started to stick,
when it did the motor made a bad clicking noise.
an old dude at the napa store told me there was only two things I could do:
1. try marvel mystery oil, he said many times that oil will help keep the valve loose. (1 qt.- half in the oil crankcase and half in the fuel tank.
2. if the mmo does not work, then you only have the following option: pull the head and have it reworked.
I had changed the oil, was running synthetic oil, that help some, but did not completely solve the sticky valve problem.
the day I added the mmo to the crankcase and gas tank the valve was sticking and making a bad noise.
believe this or not:
within 30 seconds of adding the mmo to the motor oil, the clicking stopped and I only heard it for just a few seconds one other time a few months later.
that was 3 or 4 years ago and have never heard the clicking noise again.
I change oil in the old jeep about every 2 years, as I do not drive it much.
but always use synthetic oil 10w40 and add 1 qt of mmo to tank and crankcase.
knock on wood, so far, so good,
its worth a try before to have the motor or head torn down for rebuild.
some do not like synthetic oil, but I believe it has better lube properties than dino oil, if you are having lube related problems, as you are.