Jon H’s website says application is 1967 GMC 230/250 with A/T (automatic transmission). Usually A/T engines have auto chokes. There may be a vacuum port for a choke diaphragm (divorced choke). The little info I have is that the YF-4376S has a 2-step metering rod (see attachment). Our beloved YF-2100S has a 3-step (economy, midrange, power) metering rod. Jon G nailed it about the center screw air cleaner requiring some type of adaption for older engines. In 1957 Chevy cars went to a low-profile air horn (Rochester) for hood clearance. Carter had to change the design as well. Truck carburetors followed shortly after. Some YF model throttle levers raise to open the throttle and some lower. You may have to cobble together appropriate linkage. Some YF models have a timing vacuum advance port above the throttle plate, some below and some both. Take this into consideration when setting the engine timing.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
