Step 1: Figure out a version of puppet-agent published to http://builds.puppetlabs.lan/puppet-agent/ which is close to the HEAD of the branch Josh Cooper is actively building his side of the bridge from. Hopefully this is HEAD, but might not be if HEAD is bad.
Once the SHA is identified, run puppet-server against that SHA using the PUPPET_BUILD_VERSION environment variable and see what EL-7 smoke test failures shake out.
Rinse, repeat? (Maybe as separate tickets?)