Interesting link. The AGA valve stem tool is what caught my attention. If you were trying to fix a smoking problem and pulled the valve covers to replace the gaskets and clean the vacuum hoses etc, the tool would allow valve stem seal replacement without pulling the heads and cams.
I'm a firm believer in replacing wearable components while you are in the area. This would mean that a valve stem seal replacement would only be another couple of hours rather than an extra 20 hours work. The extra effort would be worth the insurance of new seals.
Tool:
11-12-7-568-838 Valve Stem Seals | AGA Products