In your condensed version stated above, yes the building conversion must comply due to occupancy change. See Handlers input above, there may be circumstances that could change the initial outcome for compliance.
Though I do agree with Charles, I did not say it....
The "A" occupancy provisions in 1972 were under the 1970 UBC (yes I am that old). There are significant differences that need to conform to the 2010 CBC. The most difficult will be the structural requirements. Chapter 34 is the main operative code portion for the conversion "back" due to occupancy change.
All the other stuff such as allowable floor area, stories, fire resistive due to property line proximity, construction types, fire sprinklers, fire alarms, exiting and etc etc must still be done for compliance to current code.
So far, the comments have been consistent with my own interpretation of the requirements. Thank you all for your input. It provides much-needed support for consistency in applying the codes.