I have this bookmarked from a few years ago, wonder if it's the same guy
http://www.18to1.com
edit: yea it is. looked at engine bay photos, since most black GNs look the same outside.
The Duramax puts down some serious power (especially if you go for propane injection or something crazy) but the weight is a killer. extra-heavy iron block - IIRC the Duramax/Allison 6AT combo weighs in at something like 1300-1400lbs, versus 400-500 for a LS1. Pretty sweet build though, and a badass car. Check the lip on the rear wheels - hardcore negative offset.