1920 vs. Economiser

You must mean the "Economaster" carburetor by Holley. That was an after-market line sold in the late 70's to early 80's during the "gas crisis". I recall there was a 1 bbl one for the slant 6. In most, they tuned them leaner for main flow and had better fuel distributor rings in the venturi. Some people say they can't be rebuilt well because of the tinier passages.