I only made it today, so have not raced it
Friday is the day
It should work as it's 138g right accross the chassis. This leaves a little extra weight to be fine tuned on top of the chassis, 10-20g front or rear where it may need it? But the point is I have loads of spare space now.
I left the front simply trapped by the under tray. This still lets the chassis flex if it needs to. I thought that if I bolted it front and rear it would act like a laminated plate and stiffen the chassis. Just trapped at the front is fine.