Identifying Garrett turbo's
 

I got a little problem with a turbo Ive bought, I was under the impression I had a Garrett GT3076R fitted & purchased another used GT3076R to replace it, Ive partly stripped them both & found that the new one has a slightly larger compressor wheel but everything else is the same. The id plate on my old unit has gone but the new one has part num HG 6020J. Both have the same .60 compressor housing but different inner profiles, how do I identify them?