In the "Warriors of Winter"by Bill Vint there is a picture of a bubble hoods with holes in the hood on page 119.
"Three Quebec snowmobilers,Leonide Jodoin.Clerment Morier and Yvon Jodoin , drove a Scorpion to victory in the 24-hour Montpelier,Quebec,Endurance Race.The Scorpion racers covered 710 laps with the stock machine."
Notice the shrouds over the cylinders and head. That is to duct air from your fan to the cylinders. There are two types of fans. Those on the crank and those run with a belt off the crank. On the Mag side of the engine.
I know little about the hirths. A bit out of my league. ;D But there are many versions as illustrated by the above thread. There should be a tag with a model number that we could verify which it is.
I think the 650 Red Baron is one cool looking engine for what it is worth.