HKS housing would be best yes, also have a look at the .63 Garret housings, They arent the best things out there, but will be way better than the factory RB hosuing, just port the wastegate outlet and fit a bigger flapper.
You will need a new dump pipe though, or just modify the one you have.
Also re: OP6 hosuing on a R34, not all R34 GT-T's had the OP6 housing