I doubt you will find the info you are looking for, but you may. If you do let us know.
quick facts though.
Cast pistons. Good for about a 1.2 bar steady diet before the top ring land will begin to crush. Very weak and even minor detination will eat away at them. The Same applies for all the R32's and R33's. R34 has slightly strong pistons but not much.
Factory R33 GTS25t con-rods are good up to about 450hp before you risk bending them. The factory rod bolts will begine to stretch at about that point also. They also will not toloerate rpms above 8,500 before the risk of failure increases 100 fold. You can get up to around 575hp with the factory rods in the GTR before it starts to become a worry though again the rod bolts are very weak.
Rings are no were near as good as they should be either. The top compression ring has a tendancy to collaps and the oil ring break under heavy boost, anything above 1.4 bar. The rings are also cast, and I have no concept as to why either.