That is pretty fascinating...had to check out a couple Youtube vids of these things. Searched on the Vintagesleds site and found 1 guy had fought the same problem with a rusted area on a crank in a mid 70s arctic cat with a Kawasaki engine, and tried a Speedi sleeve. He was able to successfully assemble the motor, and get it idling and running perfectly. Unfortunately, there weren't too many specifics shared, and the thread ended...not knowing if it was a long term solution.
I, too, have a spare crank that has the Mag end near the sealing surface pretty rusted up.
A couple questions, that you have probably already figured out.....
1. How do you get the Speedi sleeve perfectly square on the rusted shaft..true, you can buff the shaft down to a reasonably clean surface...but a sled motor isn't exactly a low RPM gearbox....I have to wonder if the "ideal" solution is to install the sleeve and then check the runout, in the same way we check a crankshaft for runout. True enough, the rubber crank seal has some give to it, but I have to think having it precisely installed as possible would be a great thing on a shaft spinning at 8000 RPM.
2. I am willing to bet that you need to be very careful about using the installation tool to drive the Speedi sleeve too far onto a shaft. These things look like a very thin metal cylinder with a lip at one end. Apparently, you use an installation tool...which is essentially a pipe...to contact the lip and drive it onto the shaft. I bet it is a royal pain to try to tap it back if you go too far.
3. Where do you wind up placing the lip of the Speedi seal on the crankshaft? It would seem that the lip must be driven far enough to allow the crankshaft to have its correct endplay movement,and when the crankshaft is pushed hard against the Mag end, there will still be a few thousands of an inch clearance to prevent the lip of the Speedi sleeve from ever making contact with the aluminum crankcase.
This sounds like a really cool way to solve the problem, at a huge cost savings compared to having the crankshaft re-machined.
Let us know how this process procedes!