Making this fit

Nice one. Anything can be made to fit with some patience and nouse.

I would recommend a dremel (rotary tool) for working on the fibreglass and some flat alloy for brackets ans appropriate fasteners (bolts and nyloc nuts!).

I find that you don't need to use the 2 standard rear seat unit mounts if the 4 front ones are used and the seat unit is sitting on a part of the subframe at the back.

Looks like the same cbr600 rear end i have on my nc29 track bike. Like stickshift says, i used a dremmel to take some out of the front and some out of the sides "tyga" stylie. Which also allowed me to get to the fuel tap etc.
Good luck.

want to sell me the stock rear plastics?