I'll expand what has already been said.
There were quite a few production High Performance 289 specific Ford 4100A assemblies used between March 1963 and the last HP289 powered cars of the 1967 model year. HP289 engines were used in Fairlanes, Cobras, Comets, Mustangs, and several other Ford and non-Ford vehicles during that time frame. They were all more or less descendants of a Ford carburetor assembly developed for a rare 1963 High Performance 390 engine package calibration wise. Ford also used them on one hundred plus High Performance 260 engines that got into prototype Fords, Cobras, Lola GTs, and no telling what else.
All the of 1.12 bore size "high performance" carburetors were rare day one. Hot rodders usually got something from their favorite speed parts merchant. Countless units have been discarded, destroyed, modified, or parted out. Commercial "restorations" can transform a $X,000 core into a $850 mess. Some of them have become quite valuable as a complete assembly if they have never been media blasted, etched by harsh chemicals, or incorrectly "restored".
As mentioned already it is becoming very common for rare supports (a.k.a. secondary venturi, clusters, secondary clusters, boosters) to have been replaced in units for sale. Unmolested main fuel jets, choke parts (automatic or manual systems parts), and top covers are also candidates for replacement. There are perhaps all kinds of reasons and situations for this to happen but two significant ones I encounter have been harvesting and commercial rebuilding. Harvesting is removing desirable rare parts before sale for any reason. Commercial rebuilding often renders many parts forever undesirable appearance and or function wise; or rebuilders are sloppy with what goes back into an assembly. Many of the Ford 4100A assemblies are worth more as parts than they are as cores and that includes some HP289 specific models. Rare does not always mean valuable. A great unrestored C3OF-AB assembly might be worth $X00. A C4OF-AT assembly in the same condition might be six to ten times the value of a C3OF-AB carburetor.
Then there are the service replacements. Ford had to supply something for service for ten years past given production years. The service assemblies did not have to be just like original assembly line ones and they usually were not.
The C4OF-AL manual choke model was released circa late May or early June 1964. Some very late Cobras used them as did some mid 1965 Mustangs. They were offered as an over the counter accessory for Sunbeam Tigers. Many of them were refitted slightly to become a 1965 model carburetor under C5OF-L. Reworked units late summer 1964 had C4OF-AL stamped on the body and C5OF-L stamped into the assembly tag. The C4OF-AL units in complete unmolested condition are one of the two or three most valuable HP289 units. A less than great accurate restoration often decreases their value.
Bob Mannel's digital book lists many different HP89 carburetors for 1964 and 1965 production and service. Production wise with manual transmission:
C4OF-AL, used with a PCV system with manual transmission, including late Cobras with PCV and manual transmission with engines manufactured June, July, and August 1964.
C5OF-L, used with Road Draft with manual transmission
I strongly recommend that anybody dealing with 1960s Fords powered with HP289 engines buy a subscription to Bob's digital book. Bob keeps it up to date for subscribers and I refer to several sections frequently.
