Hi Keith, thanks for the plumb bob tool, sorry about your back door step!
I checked the car and the machined face on the diff is at -3 degrees exactly. There is no machined face on the gearbox that I can get to easily so i took a reading from the edge of the dust sheild on the prop end of the gear box. The dust cover projects out from the machined face on the gearbox so should be at exactly the same angle. On this i get a reading of between -2.8 and -3 degrees depending on where i put the steel rule.
So at the most the diff and box are 0.2 degrees out, would that be within torrence? To make the gearbox -3 degrees it would need to be raised at the rear by a tiny amount, a new rear mount might be the key.
My car is not on level ground, if it was the angles would be about 0 but obviously there would still be about 0.2 degrees between the diff and box.
I also weighed the allen bolts that hold the prop to the machined face of the diff. The odd one I got from the motorbike breaker is only 0.3g heavier than the others so I dont think I need to worry about these!
Let me know what you think. Lovely looking z you have by the way, cant wait to hear the noise it will make!
Ed