If you set your game to use the public_beta, you will have access to version 1.52.4 which includes Big Hurt release and Head to Head beta.
To access the beta, right click Pinball Arcade in the steam client and go to properties, then betas tab, and choose teh one that says Public Beta.
Note: To switch back to the current release build change it to Opt out of all betas if you no longer want to use the beta build.
Make sure you back up your save files first. Make a copy of this folder "C:\Users\username\My Games\Pinball Arcade"
Looking forward to feedback on Head to Head