using gasser turbo's on diesels isn't a good idea. they're meant to give boost at much higher rpm's.
if your goal is 120 hp then get a good intercooler and make sure it has lots of airflow to it, turn up the pump and away you go with the stock turbo. bigger exhaust will reduce egt's.
if you want max boost at lower rpm's, look for a K03 off of a 1.9 or 1.9TDI (early TDI as the VNT version requires a bit more work to adapt)