Risking, I reckon there is money to be made there. As mentioned above, GTR boxes are dirt cheap and GTST boxes are getting hard to find I've been told. I guess this only helps where you have a dead r33 box though and doesn't address the shortage of r33 boxes.
Uras, in a bigger car with stock handbrake setup (eg R33gtst) would you think the modded GTR box will fit? Also I remember reading about your car in HPI I think where you said you thought the R34 box was stronger than the R33 one (pretty sure it was you). What makes you think that? What are the subtle differences you talk of?
I'm certainly no expert so I'm not being a smart arse with these questions. The only thing I've noticed from the outside is the R34 box is much lighter as the casing is made with much more aluminium in the alloy. The down side is that it's very soft and easy to thread the bell housing bolts.