Yes, that hydrobooster (NAPA/Cardone #52-7918) fits 1979 - 80 C1500 with 5.7 diesel with JD3 or JD5 option code ... 6400 GVW. This matches my choice in brake calipers.
It's important to know that this particular one uses SAE flare connectors which matches my steering box and pump. There was an o-ring fitting option (52-7252) in that same year, which I'm fairly sure also has metric fittings.
One reason was the small footprint for sure, and the other consideration was low vacuum. This 454 idles pretty rough, and I want it to stop!