I just recently bought a used twin turbo, but they aren't stock and i don't think there 99 spec or BNR. The opening on the inlet on both sides is 6mm larger than stock. Plus I can clearly see machine marks where the look to have been bored out.. Cant say 100% but there is a difference. The intake hole is 1.375" in diameter.

 

Take the compressor housing off and measure the major diameter of the compressor wheel. Then look up the wheel size in compressor data charts.

-Max