Measuring the inlet hole inner diameter is a good indicator. This should be of the same size as the compressor wheel inducer diameter. The exducer diameter will be same for all T3. The trim = sqrt(in./ex.)*100 is garrett's way of sizing the different T3 compressor wheels ranging form 35 to 60 (and super-60). 2wd T3 had a trim of 50 or 55...