My /6 is running rich

The 75 should be running a Holley 1945. There are 7 variants that cover 49-state manual & automatics, CA manual & automatic, and CDN manual & automatics. Settings are different for each one.

To identify your carburetor clean off the sides and look for the data. IIRC the info should be on the side over the idle mixture adjustment screw. It should read something like 1945-R7018A . This example is for a 1975 225 w/automatic, 49-state emissions calibrations.