Number one - why are you needing to adjust your valves?
Are they hydraulic or solid lifters?
If they are Hydraulic and they are tapping bad, there is a very simple easy fix. Go to Walmart and buy a quart of
Marvel Mystery oil and pour it in yur crankcase with your oil. It will clean the lifters and make them pump up like they are supposed to and they will quieten back to normal and you will regain your lost power. I have done this many many times with success on the older engines.
If it is solid lifters you will have to go online to find out what the clearance should be and you then remove a valve cover and with wrenches and feeler gauges you adjust them with the engine running. this is messy but the best way to adjust them. I will bet that you have hydraulic lifters in your engine. After the engine returns to normal you should change your oil and install new filter and oil. Occasionally after that you should use a few ounces of oil to maintain a clean engine. Best trick I ever found for an old engine.
Dale in Fl.