Hi Steve,
interesting questions! With regard to raising the steering rack, there is an interesting discussion on bump steer here
bump steer
With regard to changing the rear suspension geo (80mm sounds like alot!) check out
GTD rear suspention mod
Re bracing the roll 'hoop' I fabricated a full cage out of 50mm CDS & took the roll bar rear stays to the top damper mounts. this was *alot* of work but will increase the safety as well as adding some stiffness to the chassis.
I've attatched a picture of the mods I made to my chassis. If I were to do it again, i would leave a bit more room around the rear of the gearbox.
Hope this helps.