You might want to search the forum for rack/rear mounts, and briggs&stratton/honda engine mounts.
Those engines are clones of the little hondas.
Look here for something like you want to do: http://motorbicycling.com/attachment...n-100_1667.jpg
You have to see if the engine has a centrifugal clutch, if not, you'll have to add one.
If you don't mind using a single-speed transmission for the engine, you can ditch the jackshaft. I think that with the 5.5hp engine you wont need gears, maybe neither with the 2.8hp one (i think the 2-stroke china kits have 2hp at most).