What sort of bearings does the turbo have? Plain bushes or ball bearings? Ball Bearings need a very small restrictor (to limit the flow) whereas plain bush turbos will most likely not need a restrictor (but some do, just bigger than the ball bearing one).
Specifically I would ask the turbo supplier/manufacturer what size restrictor they recommend.
I have a Garrett Ball Bearing turbo and bought the proper sized restrictor Banjo bolt off ebay for the turbo feed. There may be something similar available for your specific turbo.