This kind of desmo has the following characteristics:
A face-cam and in- and outside camfollowers and a coupled valve.
Outdated system and difficult to manufacture.
The ring cannot be evenly thick in the opening- and closingtrack.
I found the used camgear with at both sides cams at a jumble sale years ago.
An old-fashioned blacksmith kept it for 24 hours in his fire to temper the hardened steel cams, so I could remove the excess material to form the ring at one side and to remove the cam at the backside of the gearwheel.
Much later I discovered the side-valve engine with such camgear : The “Reading Standard” (see pic).
Nb This particular engine (watercooled) is not original (aircooled).
(Classification = Group 1B)