240z - I agree with the bushes and early 305 brakes being the major weak spots.
The diff issue is mainly the 147 GTA and the 3.2 GT isn't it? Maybe a couple of 156 GTAs? Try Googling "diff failure" - you'll be hard pushed to find an Alfa mentioned - the only mention I found was the thread here on AO.
I really don't get where you're coming from with the torque steer. Understeer is easily induced especially with ASR off, but I really haven't experienced torque steer that's noticeable, especially when I think back to the cars I've driven that HAVE suffered terribly - XR2, MG Metro Turbo, Volvo S40 T4.
EDIT:
And surely the Q2 will make torque steer slightly worse?? No, scratch that, it's late!
EDIT2: Also just realised you were saying the torque steer
DOESN'T rip your arms out of socket ... I agree - nowhere near!
