Which compressor clutch?

I’m piecing together a 351W to drop into my 67 coupe. I think I have all the accessory drive brackets figured out, have pulley alignments looking good. The junkyard compressors in possession have the v belt drive at the rear. To drive off the large outside crankshaft pulley and idler (3d forward most shieve) I need the outer face of the clutch pulley much further forward. Don lists C9AA-2981-d1 for 289 / 302 and C80E-10156-A for 351W. Best I can measure, I need the front face of the pulley to be about 3/8" overhang from the machined surface on the front of the clutch body. Both of these seem to have some overhang. The 2981 appears to have more overhang. I’ve also seen the number C9AZ-2884-A that appears may be interchangeable with 2981. I don’t want to order clutches to ‘check fit’ them, so am asking the advice of the forum. Which of these clutches has about 3/8 overhang from the clutch center machined surface? I derived this measurement putting a straight edge across pulleys and measuring to center of a belt, and looking at my existing pulley flange thickness to center of the belt (assuming they built them about the same). Here’s a nice pic off of the web of 2981. It looks like it might be correct. 10156 looks like it has less overhang.

A little bit of confusion here with the engineering numbers and service part numbers being labelled as ‘interchangeable’. The engineering number C9AA-2981-d1 is for a service part number of C9AZ-2884-D. All the the A/C clutch and pulleys have an engineering basic of 2981 and that corresponds to a service part number ( basic ) of 2884.
The second area of confusion is the C8OE-10156-A engineering number - that’s for an alternator mounting bracket.
If you refer to the MPC ( Master Parts Catalogue ) 1965 -1972 in section 24, page 24 - 26 you can find all the ‘types’ of A/C clutches and pulleys with their corresponding measurements - that would be invaluable to you if you are going on a fit based on ‘overhang’.
It would simplify things immensely if you knew which year the 351W came from. The following years have the corresponding service part numbers for their A/C clutch and pulley ( along with the ‘type’ designation:
1969: C9AZ-2884-A (type 3B ) and C9AZ-2884-D ( type 5B )
1970: C9AZ-2884-A ( type 3B )
1971: D1AZ-2884-A ( type 5B ) or D1OZ-2884-A ( type 5B )
1972: D2OZ-2884-A ( type 5B )
The C9AA-2981-d1 engineering number ( p/n of C9AZ-2884-D ) that was given to you, has applications to 302, 351 and 390.
The C9AZ-2884-A part number has even wider applications - to the 289, 302, 351 and 390.
Good Luck with getting a proper fit - it can be frustrating, that’s for sure.

Thanks GAH for the detailed answer. I’ll look at the master parts catalog to see if that gives any answers. The system is pieced together. Engine is an 85 roller cam block with GT240 heads. Some of the accessory brackets came off the 289 that was in the car, others from a wrecking yard pull I made many years ago (late sixties 351). The 351 compressor ‘pedestal’ has an extra tapped hole for the power steering pivot bolt. The early 67 bracket does not have the hole. Power steering to water pump bracket I believe is from the 67 289. These two brackets fit perfectly and align with the crank and water pump pulleys correctly. Crankshaft is the triple sheave type with large outer AC drive diameter from the 67 (factory air car). I have an original 289 AC pedestal (no threaded hole for power steering pivot bolt) and the head to compressor mount bolt relationships are the same (i.e. one bracket doesn’t project the compressor any further forward than the other. Both mount it in the same fore/aft position). Thanks again

I found a site that identifies how to properly measure the York style clutches. I’ll dig into cross reference numbers but the gist to find a replacement (aftermarket) clutch the key measurement is from the center of the forward compressor body mount hole (4 big holes) to the center of the nearest pulley groove. Then clutch diameter, number grooves, voltage/plug style etc. Maybe this will help others in the future.

After more digging…industry standard seems to be the term ‘clutch mounting distance’ or ‘gauge line’. This is the distance from center of the v groove to the center of the forward (2 of 4 holes) York compressor mount hole(s). Rock Auto listing for 67 289 the Four Seasons clutch 47809 indicates a distance of 2.875. The same compressor is listed for the 1969 351W. 2.875 indeed does match the pulley center alignment of the Frankenstein mounts I have. I was not successful in finding a cross reference from the FOMOCO numbers to any currently available items. So can’t say if 47809 is the same as C7AA-2981F. But it likely is. Will update this post later.

I spent 30 seconds on eBay to find this one. 69 MUSTANG V-8 302 351 ORIGINAL FORD AC COMPRESSOR CLUTCH & FIELD ASSY CORRECT | eBay

I understand Royce. I looked there too, even found a NOS clutch with the 2981 part number. My issue was that I’m mixing parts from multiple years and there are so many FOMOCO part numbers it’s not easily possible to know if all those part numbers are functionally the same, or if there are different ‘clutch mounting distances’ (resulting in placing center of the v in a different position fore or aft). Tried to buy from the WCCC catalog to support the enterprise but there are two different part numbers. One that was pulled from a 351 and another from a 289. So, not just wanting to buy without some sort of engineering confirmation I dug in. In the end…you are right, I could have just risked it and bought that listing you identified. I did buy one off Amazon that’s the same thing, but now I’ve (we’ve) learned how to measure the clutches without guessing you’re going to get what you need. Thanks for your research / help. Cheers, Hal

I have not had a big problem finding compatible 289 - 302 - 351 - 390 - 427 - 428 AC clutches. Seems like the ones I get always work.

I likely over-complicated it. Thanks again Royce.