In some cases A upgrade kit if completely done can be spotted by lifting the fuel tank and looking at the ignition Harness to see if it has the updated plug.
Anyway by the book at 16 mm that gauge they send you would bottom out on the shoulder that is 16 mm, at that point they insert a spacer .390 inch by .355 inch, you can use a 3/8 inch or 10 mm bolt shank cut to .355 inch long. this increases the tension on the spring helping the adjuster work and hopefully not kick back.
So once you pull the center nut you will see a shoulder just down in on the plunger. In the view below for vision you are measuring the drop between the two arrows
if this drop exceeds the 16 mm the spacer goes in but they do not tell you what if anything after that. so the plunger only drops 25 mm well .520" to be exact. so if your plunger is way down of course add the spacer but be aware as the tension pressure is really decreasing especially if the plunger is bottoming out. This would indicate guides and at least chain. the gears on the cams most likely are good Still.
Are you versed with using a dial caliper? not to be a smart arse but not everyone is a machinist so I ask in case I need to provide you some measuring pictures?