I have been looking for this information for many years.
This is critical information if you want to interchange
compressor housings.

The C diameter dimension is the critical diameter.
If this is the same as a new compressor housing chances are the new one will
fit.

A lot more on this in the future.

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Correction!!! Wrong! This info is of no use.

Garrett totally renamed and re numbered
their entire line a few years ago. My guess is they failed to copyright the names years ago and some Chinese company started selling TO4 rip offs.
Unfortunately this had unintended consequences and created havoc in the
after market field. It is no longer easy to mix and match compressors, bearing
section and turbine housings if you have a TO4 or some other old Garrett turbo charger. There are some old guys out there in the biz that know. Turbonectics
was sold out to Kelly Aerospace and all of the old owner's  info became unavailable. Several books were made irrelevant over night.
The most famous of which was "Turbocharges" by Hugh MacInnes.

Bottom line! I was unable to install the tach using the info and dwgs that
came with the Garrett kit as they were all referenced to new Garrett part numbers.

Rhino to the rescue. I was very carefully able to duplicate the dwg
of the stock 2nd gen compressor diffuserr by  measuring the reference diameters and plotting the curve. Then Rino lofted the reference diameters at a click of the mouse.

This then allowed me to make a dwg giving the info I needed to install the tach
sensor.

SAVE THIS DWG and MESSAGE. YOU WILL NEED IT SOMEDAY.

Paul Lamar