Center Housing Rotating Assembly, The middle part. You can see the tag in this picture. Just wipe it off with a rag to read the numbers. For instance the tag on my GT30 read 700177-5023 (I still have the tag, but not the turbo) and I can look that up on Garrett's site to see the specs.
TB water lines should be the two on the bottom of the TB coming from your water pipe. Just divert and run longer lines to put the turbo in the loop.
TB===engine
TB==turbo==engine