Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
Sorry Graham but your wrong here. If the parts were identical then it would have the same part number, there are NUMEROUS examples of Honda using the exact same part on lots of different models but they still kept the original part number. There are websites dedicated to cross referencing part numbers, showing all the models that part number was used on. The 250N master cylinder was a single disc MC not a double disc, if you look at the 400N (45500-443-614) which did have a twin disc setup it didn't use the same part number as the 250N (45500-442-612) yet they would have looked identical, yet they were designed to do a different job. So it looks like you put an MC onto some CX500 which if they'd had been in an accident, and it was blamed on the wrong one being fitted, you'd have been liable I'm not saying that sourcing where the parts were manufactured originally means your wrong to fit them as they don't have the Honda part number on the bag, clearly they are the same part, as such they are fine to fit. However it's wrong to assume that just because a part looks the same as another it's the same part with another part number, Honda just didn't do that, especially in the 70s.