Brian, several of these were, and are used on mini bikes with the mount you have pictured. The early Stellars that were sold as a "Scoot Along" had Clinton A400's on them, or were available like that. (I am doing one of those right now, in a regular Stellar Compact Frame)
You don't need a jack shaft just because it's a two stroke, unless you cant obtain clutch and axle sprocket to get you at around 9 to 10 teeth in the front, and around 60t in the back with that engine. (You can get a clutch) The torque is where it lacks, so you cant over gear these. But the payoff comes in the higher RPM band. I wont insult you by quoting gear ratios, since you can find them everywhere.
I used this engine on a fun kart and it powered it pretty well, given my weight. The decision you have to make is if you're going to run a JS, or turn the rear hub around. I noticed on my two-piece Stellar frame that it will have no clearance issues either way, as far as the rear wheel. However, a jack shaft completely changes the look of a bike as you know, and is pretty invasive as far as modifications to vintage bikes go. (A personal decision)
One other word of caution- that exhaust sits in the way and prevents several applications of exhaust pipe to work with mini bike frames. With my engine, I will have to run a jackshaft just to change the angle of the drive chain, so I can clear that high dollar and very cool vintage exhaust pipe.
Run it at 20:1 and do not set it to run max lean at high RPM. The extra power is not worth destroying that engine. I hope this helps.
