That manual would be a great help, but be advised, it's a parts manual. It may not offer the technical info you are looking for.
I believe you need an NKG BR-6HS plug (comes with a. 028" gap), but that is based on an old Arctic parts number. It may not be accurate. I'm checking with a couple of friends who would have the answer. Jeff Mihalko would probably know as well.
The Kitty Cat snowmobile used a T5A, a smaller version of the T6A. Specs might be the same.
T5A specs a BR-6HS plug with .020" gap and point gap of .012"-.016". 20 degrees BTDC