metal filings are always a scarry thing to find when draining any oil sump.
if you don't have a magnetic element ont he oil plug I'd go buy a small button rare earth magnet and stick it on there anfter cleaningthe plug.. glue it on with a drop of superglue.
now then.. for a flush? I have usually flushed my old fords with a mix of atf and diesel when i get then as a baseline to get all the old oil out.
your call if you want to do that or not.
past that.. refill with good oil, and service again if you notice any odd noises or differences in handling.. and then see if you are getting more metal shavings.
if you are lucky, it was either not serviced and those are left over from the manufacturing process.. or it was just accumulated incedental metal from the gears.
soundguy