Brian,
Best info I could find. The Cat RV Recommendations sheet for my coach only shows the IR0751, and no primary water separator filter, which is why I first referred to the Racor 200200 that Beaver listed in the Chassis manual. As I understand it, the engine mfgr normally lists 1 filter and the chassis mfgr, adds the other. A search on the web shows that both CAT filters are rated at 2 microns. The Racor 200200 and S3230P filters are rated at 30 microns. I wasn't able to confirm the FS-1287 used in my coach but it crosses to a NAPA filter that has a 14 micron rating. What filter number are you replacing?
Steve