DId you look through all the posts on OCC bikes? There's a ton of videos on youtube with OCC bikes, just search OCC bikes or OCC motorized bikes, you'll get a whole list. Most of the vids suck. How many times can you be told,"This is a gas tank, this is a throttle VROOOM VROOOM." until it sounds like it's going to blow it's guts out
but you can look to see what others have done.
I think Dave31 has mounted the sprocket direct to the hub by drilling for the 9 bolts. There are two bolt circles for the sprockets and the smaller diameter of the two will allow something like this. I got one of those for my current build but had to drill it to the larger bolt circle. I've looked for a post on how he did it but haven't found it. Maybe he'll post and we'll all see