Fun to watch someone work!
On the lighter valves..... the difference may be in the lighter valves having the 'dimples' in the valve head rather than being fully flat. Saves weight, but they will increase the combustion chamber volume by several cc's if both the intake and exhaust have the 'dimples'. (I recall measuring 2-3 cc's increase in a 273 chamber with the 'dimples' vs/ without.....)
