Depending on the cost of lifters. I test lifters in my drill press. Just put them in a tray of fluid and see if they pump up and pretty much hold. Each one on removal should have a location mark put on it.

Why especially on your engine? There has been mention of the oil feed passage to the lifters being blocked. Partially obstructed is a better guess. After a test taking them apart cleaning and retesting them. You can buy one new lifter for comparison purposes. The ones that test as new if any after. Your call then.

Again what to do can depends on cost and circumstances. For example If I found after proper internal cleaning they were testing as good as new. I might reuse them if really expensive otherwise. Now if they all test good right out of the engine. You might think their oil feed is involved. The day where I got a set of new lifters for 15.00 for a chev engine is long gone.

As mentioned first starting with some type of cleaner. A bottle of miracle mystery oil in the base oil could be additional to whatever else you try. They make a big deal out of its ability to quiet lifters sometimes. Nothing is going to quiet a worn lifter though. Built up varnish and buildup on the valve port inside the lifter being cleaned I can see. If the car has been on a diet of synthetic oil it has some cleaning ability itself compared to dino oil.

Or if you decide to buy a new set before starting. Rather than just throw the old lifters. Try testing them for experience at least.