dead hoot clutch wasn't hard to remove
When my Hoot clutch died it wasn't hard to pull out. Mine was help in with an allen-head bolt, which I unscrewed doing something like what Mike recommends. The remnants of the clutch bell slid right off, and I pried the clutch out with two screwdrivers and just a bit of wiggling.
As an old bicycle shoppie, I'd try heat like Houghmade recommends (but keep the flame away from your gas line) and then probably some good penetrating oil and a lot of light tapping, like you're laying down a latin backbeat. If this doesn;t work (and it sounds like it might not) and you wipe the bolt head out enough, you might need to drill the bolt out. You could try to save the existing threads by drilling a small hole in the the center of the bolt and then very gently mushing the remnants into the cavity. Another way that's probably just as fast if you already own a thread tap set is to just drill the sucker out without worrying about keeping the old bolt size and then tap new larger-diameter threads in the motor shaft. Given that the shaft is 5/8 inch (or turned down to about 0.550 like mine) and the bolt is much smaller, there's more than enough metal left in the shaft.
One thing I caution against is getting fancy with a bolt extractor, which is a cone-shaped tool made of very hard metal, probably about as hard as a file and about a brittle. You drill into the bolt, then screw the extractor in, which in theory at some point binds into the offending bolt and removes it. In practice, in small bolts the tip breaks off in the bolt, in which case you have a piece of metal harder than a drill bit stuck right where you want to drill further... Then you have to go to the step of drilling an even larger hole than you'd have if you just decided to drill and tap in the first place. I'd skip this step and go bowling instead.
Then, after all this is done, make a nice piece of wall art of out those quaint Hoot gears, and buy a Grubee, or build yourself a belt / pulley drive. Simpson is working on one, which is undoubtedly a more professional version of what we used on our go-kart built from a riding lawnmower back in 1976.