245 = 9mm commerial production.
PP = 88 as in 1988 production.
5 digits = sequential serial number.
It
is a MkII…FN manufactured them between 1981 and 1989.
FWIW, FN replaced the original rowel/ring ("Commander") hammer with the current spur hammer circa 1971 to address "hammer bite”. The spur hammer has a thinner shank than the "Commander" hammer. If you replace the current spur hammer with a production "Commander" hammer, you'll more likely worsen the situation.
There are, BTW, 3 versions of "hammer bite", pinching the web of one's hand between the hammer shank and the tang, slapping the web of one's hand further back with the spur or ring portion of the hammer OR a combination of both. Hand size/shape/position/grip usually determines which, if any, version of "hammer bite" one might experience…BHP “hammer bite” is certainly NOT universal though.
Often, simply shortening the length of the spur by 2 serrations will eliminate "hammer bite". Some folks also bevel the lower edges of the shank. Done sparingly, all that's then required is degreasing/warming/touch-up bluing.
Another option: C&S makes a "No-Bite Commander Hammer" with a thinner shank and smaller ring than the production “Commander” hammer. It eliminates “hammer bite” as is…for most, but not all. Keep in mind changing either hammer or sear independently can cause hammer/sear engagement issues...or not. C&S also sells the "No-Bite Commander Hammer" with a matching hardened sear which often requires little to no fitting.
Or you can sell it to someone here who'd keep it stock…and cherish it for what it is
.