Guys,
Back when I raced my CJs, I had the plugs removed and replaced in 20 minutes per side. Yes, with the valve covers and smog tubes in place! Don't get me wrong, it took years to perfect this technique. I used long extensions, short extensions, and swivel sockets. I 'found' the sweet spots aka the best angles to remove/replace the plugs. In my experience, the most difficult was the spark plug wire removals (without breaking the ends), and getting them refitted on the plugs. As mentioned, removing the valve covers and taking your time on this job.