My plan was to put these on both the front and rear since they come with the solid bushings.

I am now being told by two vendors that the Cup arms are 20mm longer than the TT arms and that if I did this, the rear camber might be too much in the rear.

Has anyone put the cup arms on the rear of TT and not been able to dial the camber out enough?

 

I have these on both the front and rear and have replaced the factory bushings with ERP hardware. My tuner had to shave a bit off the sides where it bolts to the subframe to make it fit on my 997TT. I'm running 1.5 degree negative camber right now. I'm not sure if they cut any length out.

The 997TT stock arm is on the right in the first and third pictures.

 

You can actually use the solid gmg adjustable thrust bushings in your stock arms. I have cup front trailing arms on the rear of my car. I would suggest a race oriented shop like gmg or farnbacher-Loles that did mine.