Rich, I went ahead and pulled the trigger on Amazon. No since in throwing away the rest of the kit.
Keith : I think you made the correct choice. Not just because of the fact that you'd be throwing away perfectly good internal parts that you couldn't use, but also because of the seats themselves. In your specific case, it sounds like you have your known original Master Cylinder, and would thus be able to confirm that the Kit seats matched those in your existing MC. However, for others reading this thread, that may not be the situation. Case in point ; on my '67, which my Dad purchased from the original Owner in 1981, at some time, the original MC was replaced ; either by the PO, or even possibly by my Dad (although I don't remember him doing so). I, wanting to replace the Wagner MC with the original Bendix one, sought to find an original Bendix casting. In my case, with original Drum brakes, I was also going to add the Optional/ Accessory Booster. As I noted previously, the Manual Drum Brakes and the Power Drum Brakes both used the same 2227061 casting. I purchased one from one of our members a couple years ago, and when disassembling it, compared the parts with those furnished with the original C7ZZ Kit that I had, as well as with those on the Raybestos Kit. All of the parts in the two Kits seemed identical, while the tube seats were slightly different ; the orifice size in the C7ZZ Kit being 0.0116", and those in the Raybestos Kit being 0.110". However, the seats in the MC that I had purchased, were 0.089". While 0.021" diameter may not sound like much difference, since pressure is a function of Force divided by Cross-sectional Area, this could make a difference of almost 35% in the resulting pressure. While this may or may not affect how the system actually functions, one would think that you would want to replace seats that had an orifice size at least close to the original ones.
Being curious, I wanted to find out just what application(s) this Bendix casting (2227061) might have had. The source I had, showed that this casting was used on 1967-72 Fords and Mercurys, and 1967-73 Fords and Mercurys, with the two applications showing different Master Cylinder assembly Part Numbers ; one for Manual Drum Brakes, and the other for Power Drum Brakes. Based on this, plus the fact that the used MC that I purchased came with a rubber boot and brake push rod, I concluded that it must have come from a Manual Drum Brake application, Mounting and tube nut sizes for the lines were identical in both cases.
While checking on castings, I also decided to check on the one used for 1967 Mustang Power Disk Brakes (2227161). In this case, things become more complicated, especially if one does not have a known original with which to compare (thus the reason for this long Reply). The 2227161 casting was used on 1967-72 Mustangs, 1967 Ford Trucks, 1967-71 Chevy and GMC Trucks, and 1967-70 Dodges and Plymouths (again, each set of applications shows a different Master Cylinder assembly number). Thus, besides possible internal differences, there are likely physical differences in mountings and in tube nut sizes.
So, a "word for the wise" ; if taking Richard's suggestion, "If you are ONLY needing the seats, you may still be OK", just be sure you have a known 1967 Mustang Disk Brake MC with which to compare, and even more importantly, if you don't have an original, and are seeking one, be sure that it came from a 1967 Mustang. At least through 1968, the Power Drum and Power Disk Brake Master Cylinders were all "unique" to 1967 Mustangs, all carrying a C7ZZ Part Number, and the Manual Drum MC being unique with a C7ZZ Part Number until January 9, 1967, at which time it was replaced by C7AZ-2140-M.
Hope this will help some from ending up with incorrect parts.
Bob