With more fuel the stock turbo on a 6.0 can make over 500, and over 700 on spray, Its been done plenty of times. There is a guy making modified turbos (Mad Turbowerks) who just started the venture, he started with these duramax half breeds, and his latest project is dwarfing a 4094 garret turbo aka the garrett stage 2 powermax, and making it a drop in for the 6 liter. He machines the exhaust housing to fit the new turbine, and uses the guts of the 4094. He's a total maniac.
The duramax and 6.0 turbos use the same frame, just the LLY compressor is the same dimensions of that of the 6.0 powermax garrett offers at 63.5. inducer/88mm exducer. Do do this you need the compressor wheel, backing plate, and the compressor cover. Surprisingly the vband compressor inlet fits the stock 6.0 intake boot and slides right over, however the backing plate needs to be welded to line up with the bolt holes. He also makes a few tweaks to them to make them not surge or have dead spots the powermax is known for.
Hope this helps