There are many different incarnations of the TD06 20G. There is a TD06-20G, TD06H-20G, TD06N-20G, TD06S-20G, TD06L-20G and TD06L2-20G. Then there are the optional turbine housing sizes as well. There are 8cm, 10cm, and 17cm housings available for the 20G based compressors. So there are 6 different turbine wheel options to mate to the 20G compressor plus the 3 housing options. There are also compressor housing options but the 20G wheel performs about the same in all of them, even the little TD05 based housing.
There are also different versions of the 25G (T67) although not as many. TD06H-25G, TD07-25G and TD07S-25G. I think there is one more but I'm not sure of the name. Turbine housing options for the 25G are as follows. 8cm, 10cm, 17cm and 22cm. So 3 or 4 turbine wheel choices and 4 housing choices. The 25G is available with a 4 inch inlet or 3 inch inlet on hte cover.
Some of these may not apply to your application but maybe helpful for the archives or just in general.