Ac help and What is this part?

I have a 1972 Demon with factory AC with the same grommet. One vacuum line goes to the vacuum canister to supply vacuum to the interior controls, and the other goes to the heater control water valve. I also wanted to replace my heater core. I bought a new one that was close, but just didn't fit. I put the original one back in. Did you get the HVAC box rebuild kit from Detroit Muscle? It worked awesome on mine.