Use the following Chocolatey package to install OpenSSH for Windows: https://chocolatey.org/packages/win32-openssh
Once you've installed Chocolatey, running the following command will install what you need:
choco install -y win32-openssh -version 2016.04.05 -params '"/SSHServerFeature /KeyBasedAuthenticationFeature"'
You need to configure authorized_keys on the Windows agent by creating a .ssh folder under C:\Users\<username>. In this folder create authorized_keys and paste the OpenSSH public key that you obtained from Passphrase when creating the Credential.
Add the files in https://github.com/RedpointGames/phabricator-extensions to your src/extensions/ directory.
Follow the exact same setup instructions as the main Drydock guide, except use the "Windows Hosts" variant of the blueprints.