Its just experimenting, plus he is light weight so it sure is doable he uses a 43 fin he said with the 8,6 ,yes 40 years ,
using a 7,5 on the 67 is easy ,it is rated up to 7,8 ,the 67 is a stand out board ,so quick to plane
I'd have to say its the best slalom board I have ever owned ,mine has 113 litres vs the new 2024 @ 110 litres ,and glad for that
being a 98 kg rider.I asked Marco Lambers about sail sizes he uses for the 63 ,he mention he uses a 7,5 on it too .

the 63 seems to me like a longer board with slightly less rocker so I might try it one day on mine I have only owned it for 3 months
.my 92 Patrik is very comfortable
with a 7,0 ,you just have to have a solid steady breeze to keep it out of the water ,I use a no cam 7,0 with a 34 weed fin
up in Shark bay with it ,its not a nice board in chop quite a flat long rocker line but goes like hell .