Thnx NotATether, Ive tested it with few mpk/passwords generated with 3 old blockstack versions (0.10.x) and with that simple code I got the same public/privkey (also added WIF for easy import to electrum).
I am having difficulty installing the required dependencies of your script (module registrar and all its dependencies) alongside blockstack, and as I predicted it is very difficult to find a virtualenv for python2 in the ubuntu apt repositories

Can we not make this script use python3? Yours doesn't depend on blockstack-client so it's possible as long as registrar has a Python 3 module.