Hallo Mike!   
      
    MP> Is there not a "pure 64 bit" raspbian distribution specifically   
    MP> for the RPi3?   
      
   Not that I am aware of.  As far as I know about it raspbian is resisting 64   
   bit development in order to keep the distribution compatible with all the   
   raspberry pi's up to and including the 3b+ which is the latest and greatest.   
      
   Het leven is goed,   
   Maurice   
      
   ... Huil niet om mij, ik heb vi.   
   --- GNU bash, version 4.4.23(1)-release (x86_64-bonnell-linux-gnu)   
    * Origin: Little Mikey's EuroPoint - Ladysmith BC, Canada (2:280/464.113)