[68gmsee]

I have done it both ways. I'm an old timer and learned from working on engines with friends way back in the 60's. The first time I replaced hydraulic lifters the recommended way was to adjust with engine running: Turn the adj nut out until lifter starts to click, tighten until clicking just stops, turn adj nut in 1/4 turn increments. Wait after each 1/4 turn until engine smoothes out before next 1/4 turn and do it 3/4 turns.

The new procedure as HEi mentioned is by far the easiest and least messy. On a new rebuild it's the method I use. However, old ways are hard to break and I have to admit every now and then I do the engine running method if I just need to replace valve stem seals on an engine that's not being rebuilt. I use the valve cover method and I also have clips that I can use if needed.