He's referring to machining out the 13C compressor housing, as it fits on the TD04HL series as well, which allows you to keep the oem actuator and look, here's mine which I did together with TurboDutch (Left 18T, right 13C original).
I would opt to go with the better TD04HL hotside and a 15G/16T compressor. I've also ran a 13T which are easier to find with oem everything for 220hp at 1.0 bar of pressure with chipped LH2.4, which is about the safe maximum on that setup. Kinugawa also sells kits that bolt up to the 13C to switch out the compressor side, but that is a mismatched hot/cold side IMO. Here is a picture of how I clocked and made a bracket for the 13T: