1320 is the flywheel side and 003-1972 is the clutch side. There's also 9640-951-1972 used for the clutch side on saws with cat mufflers for whatever reason -- likely heat related. Probably doesn't apply in your case. Both seals are the same size.
And it's a 10mm saw by all indicators, though I believe there are 12mm slant fin top ends floating around out there these days, too. The serial number says it should be a 10mm small end rod and wrist pin saw. Can't help with the date, but guessing somewhere between 1988 and 1992.