Since I'm having issues with my '75 300, I've been doing a lot of searching for carb diagrams and settings tips.
Found this link to be helpful. It has a diagram and some guidelines for setting the carb.
http://ryan55349.tripod.com/johndeeresnowmobiles/id54.html
Hope this is helpful to someone. Also, if the info on that site isn't correct, please post here.