Tony,
With the supporting mods you have it would be fine, do you have greddy cams and adjustable gears or just adjustable gears? I would suggest cams or at least your standard cams dialled in to get most of the larger turbo. I know of R32 GTR's running between 300-350kw at the rears with T04z, 260's cams and standard bottom end. Also running 11sec1/4s on Pumpfuel. Expect full boost around 4,500-5k and it will take off like a jet from there. I probably wouldnt run more than 19-20psi on the standard bottom end, and with a good tune.
Keep in mind to change to single turbo you will also need the following:
*Turbo Manifold to suit single T04Z turbo (6Boost are around $1,000, HKS are $1500+ or Ebay for under $450)
*External Wastegate -44mm or larger, id personally go a 60mmV-Band (HKS $1000, or Ebay $250ish)
*New dump/front pipe and screamer/wastegate pipe (Would have to be custom)
*Bigger injectors, Walbro 255LPH intank Fuel Pump
*New intake pipe and airfilter setup to suit single turbo
*New/modified intercooler piping from turbo to intercooler
*Larger AFM's if not running MAP sensor type ECU
And last of all, dyno tuning. Would still be cheaper than buying a full HKS kit etc, if you buy the right parts to match it.