I wasn’t at a complete standstill though. While I was endlessly debating the sissy bar , the fork length and the handlebar rise (not to mention how i was going to attach the handlebar) I was making progress on the other parts.
I made a pattern out of hardboard 
Laminated a bunch of 3/4″ MDF scrap together. 
Then used a flush trim bit to shape them 
Used the same pattern for the doors
I decided to mortise/tenon in a different kind of sissy bar.