I've had trouble removing these as well. I'm sure that there is a puller available. What I have done in the past is remove the nut and everything that holds it on. The ones that have been on for 40 years are usually stuck pretty good and don't just fall off. What I do is find something cylindrical and made of hardened steel (usually a piston wrist pin or deep well socket) and put that in the hole. Then I put the big nut that was holding in on back in. As you thread the nut in, it should hit your pin or socket and bottom out (you may need a couple pins). Now as you continue to turn the nut, the pin will push on the crankshaft and push your clutch off. If it is stuck on really good, you may need to temp cycle it a couple times. Heat it up, throw some snow on it, heat it up, throw some snow on it, etc. Good luck!
I rebuilt my eltigree 6000 last winter and had troubles pulling the comet off.. found out from a local snowmobile wrecker, GM penitrateing fluid works really good.. So i tried it and it does..
soak the inside with the GM penatrating fluid, and then do like mentioned above, with the bolt and pins... But put tention on it and then leave it for awhile... go back and tention it again. took me a few hrs of doing this but it did break lose. The clutch was rusted on pretty good, but when it did pop lose, u could see where and how the pentitrateing fluid had worked its way into the rust and losened it.
I had tried the heat cycle thing and it didn't work for me.