I'm not an expert, but I don't think an HX50 is configurable. Meaning, it is the compressor and turbine sizes that make it an HX40, HX50, HX52, HX55, etc.... The HX50 is used on slightly larger Cummins engines such as an older L10 model. You could get one cheap from a used truck parts yard. Put a kit in it and have a good genuine turbo, not a Chinese knock off. Cummins also used them on the 8.3L in applications where the engine made 300hp or more, most commonly marine. Could start here to learn more:
http://www.myholsetturbo.com/modelinfo.html
People that really juggle turbos say that Holset are on the lagging end of technology, and that almost any newer Borg Warner S series or such will do circles around them. I don't know, maybe? Another thing to look into depending upon how serious you wanted to take the replacement/upgrade.