Hypergear can stuff pretty much any core you want into the stock turbo housings, but you don't want to go too big unless you plan to tune the car. One of his highflows has recently hit 280kw on 98 on a M35, all in by 3000, but the same turbo on a Skyline can go as high as 330-340kw on a highmount manifold, so our stock manifold is a little restrictive it seems. (plus auto losses)
With a switch to e85 there is an easy 300-350kw with a cheap highflow upgrade, and the engine will take it all day. (The gearbox won't take that for long without building it though.) As usual Nissan over engineered the engine for longevity.