If I understand you correctly it's easy.
We set the Project Number in Info (File / Info / Project Info) under item 3 (Project Number) which is stored as #Pln
The Drawing Number is assigned in the Layouts Navigator in the top left hand box of the 'Properties' window, and is stored as #LayID
Drop these 2 variables into your title box, adding any characters you might want as separators (e.g. we use backslash: #Pln/#LayID)
This is then the appended to the drawing title when the drawing is published as a PDF, except that in our case we always get a warning message that the backslashes have been converted to underscores because the operating system doesn't like backslashes!
Hope this helps.