Thanks man!
Since installment of the 25,5mm torsion bars I have felt some severe trembling of the wheels when doing a burn-out on a less watered surface.
The extra brace from fork to cage didn't make a difference either, so I concluded it must be my now 20+ year old Bilstein gas shocks not up to the task of controlling my thicker torsion bars.
As Santa Pod is rapidly approaching as well as Time Attack in june, I opted for the shocks that Porsche delivers with the M030 option afaik on the 944T: Koni yellow-Sport shocks. They are a safe bet that they will match the torsion bars, are oil and gas filled and single adjustable.