Well, actually the 157 and 160 tooth flywheels are for the 289s. The 164 tooth flywheel is typical of the 351W and 351C engines. At this moment, I'm holding flywheel # C3OE-6380-B which is straight off of an original 65 289 stick shift Mustang. It has 160 teeth (counted and recounted about 50 times). I'm using the aluminum bell housing from that same engine on the 5.0 based stroker (5.0 type 157 tooth flywheel) in the Fastback.
Bernie: my book doesn't list that flywheel as original equipment for the Mustang, although it does list one 6380 as a casting #. The rest of the casting #'s and basic part number is 6375. The one listed 6380 version is for a 428 or 428PI for 68 Shelby.
Yea, I know... My reference, which I don't trust all that much, doesn't list any "6380" flywheels. It does list a 160 tooth flywheel C3OE-6375-C for 63 - 66 289s. Maybe it has something to do with casting nos. vrs part nos??? However, I do know where this 289 came from (65 Fastback 3sp. stick) and it had never been apart. I pulled the bellhousing and flywheel off of it myself. Obviously, its not likely that a small block 28 oz. flywheel with a 1963 part no. would be used on a 428. I guess its just another Ford part number mystery!
I don't think I have ever actually seen a flywheel with a casting number of 6375, just about all I have seen have the 6380. I too have some of those books which say they should have 6375 part numbers. I have an originall Ford 65 Parts and accesories catalog, the 6375 seems to reference the part/engineering number(like what may have been on the box).The same catalog also show a replacement ring gear -part number C20Z-6384-A, 160 tooth, 13.25 inch diameter O.D. as servicing all the manual V8 289 Flywheels used in Mustangs and Falcons.But whatever, the 157/160 tooth count flywheels go with the small aluminum bellhousing-casting number C5DA-A, there is also an early aluminum large bellhousing-C5AA-B-it takes the 164 tooth flywheel. Sometime around 68 with the 302 J code motors the C5AA bell became more prevelant, and in 69 with the addition of the 351's a large cast iron bell which worked with the 164 tooth flywheel seems to have become the norm.It had casting number C5TA.
If it was an aftermarket flywheel. Also I think in order to run an 11" clutch (like I do in my 66 conv) you have to run a 164 tooth flywheel, I use one (164 tooth) in conjunction with the C5AA large aluminum bellhousing behind my stock 289 with toploader 4 speed.
I guess I'll have to email the PO and see if he knows. I don't think or know of any way to tell what size flywheel or clutch w/o taking everything apart. I don't want to go buying a flywheel unless I know for sure it is the right one.
Bernie Frank said in his post: "Well, actually the 157 and 160 tooth flywheels are for the 289s." I agree, as I also have a 160 tooth flywheel in my 66. I too counted and recounted at least 50 times, as I was told and read that the 289 only came with a 157 tooth flywheel.
Either the 157 or 160 tooth flywheel will work as long as it has the 28 oz. imbalance. This implies that you also use the "small" bellhousing and associated block plate. This is not to say that the 164 tooth, 28 oz. flywheel wouldn't work, but you would need the "larger' bellhousing and block plate. The small setup was typical for 289s.