Agreed, certainly a 2F, but no RPM present. I've seen the filled S on several other reverse dies, besides RPM-001. The dies saw so much use this year that by the time they hit LDS they had all kinds of issues. RPM-001 (FS-501) is the easiest to spot. The others I've had trouble picking over the years, as the second MM often becomes a blur in the Die Deterioration. I believe I only have 2 of the 4 for this year, FS-501 being one of them. The rest have evaded me. . . So far.
Edit: 5 total RPMs for that year, left out one Wexler has listed.