I'd agree on the hot exhaust. It's an old joke amongst vintage sled heads to race a group of wankels across a lake and see who can light a cigarette off the glowing stainless header. The 303 header would glow if the sled was run hard and also jetted lean. The engine can burn down, like a two stroke, if run too lean. I jet mine on the "as rich as I can run the thing" side, use good fuel and synthetic oil. Still don't freak out if the header glows in the dark after a 10 mile flat out run. If the thing is glowing all the time, yeah then freak out. This means either the jetting is too lean or the timing is too far advanced. Timing creep is something the later KM24 engine was famous for. Other funky problems the engine had, were some would allow chaff from the fields to creep into the points and burn onto them. Then the engine ran like crap. Dad only had one, a 68 or a 69, do this. I remember my 71 and 72 did not do this. But the big beech with the '72's is the hood allows snow to blow right into the carb if you go powder busting. That makes it choke off and ice up. The other problem was the Tilly HL carbs can be an annoying POS. They run good for about a year or two, then need a complete rebuild. I have hit that time again with my '72. I am thinking about going with a HR/GEM hot rod intake swap. Gives it a bigger carb, more power, less chance for icing if I make a hot air snorkel rig that takes warmer air off the block. We did this mod back in 1974 and it did help a similar sled I had back then. GEM is long out of business, but the manifold adaptors show up at swap meets every now and then. The carb we use is a HR off the Kawasaki 292.
If my memory is right, I think it added about 5 mph on the top end, and power in the upper mid range to top.
That sled would walk up a tree as far as hillclimbing goes, with that 17 inch wide cleated track and three feet of it on the ground, if you threw on about three boxes of Kalamazoo super claws.
Several years ago we had a blizzard that dumped three feet of powder out here. My neighbors new sleds kept freezing up and could not break trail. I kept stopping every 30 minutes to let the carb thaw out, but the old wankster would not get stuck! About the only sled running that night.