Magenta is the a-arms and upright, green is the superstructure to mount the a-arms, yellow is the new fuel tank position (surrounding the air box) and blue is what you could cut the rest of the scooter down to for lowering the rider. You'd need a steering head for the bars and steering links to the upright and probably some structure for more forward foot pegs
It looks like a Burger 650 is about 600 lbf dry, which seems like at least 200 lbf more than it needs to be, especially for a single rider.
I thought about getting an AN650 to do something like that but the small tires, high wait and the general high price put me off.
Here's a concept around an SV650 with no rear cylinder and Hossack FFE. The rider is probably a bit low for good chain clearance at full bump. The SV has full-sized 17" wheels vs the smaller wheels on the AN650:
You can see how the nose can be a lot lower if you eliminate the tall teleforks and lower the rider.
cheers,
Michael