If you think that the piece/s came from a rocker arm needle roller then.
Remove each jesel rocker arm, disassemble & inspect for a/any missing needle rollers.
If there are not any missing, then you can eliminate those parts as the source/s of the metal fragments.
I'm 100% POSITIVE that draining/adding your oil was NOT the causation of dislodging any metal particles, as HARD cornering/acceleration causes a multitude of MORE FORCE to dislodge a metal particle/s then the rather relatively benign action/force of draining/adding oil.
My approach would be this...Check the roller rockers for any lost needle rollers. All needle rollers intact, then proceed to inspect the cam shaft gear, that's intact, then thoroughly inspect the rest of the internals, using compressed air, blow out all passage ways & clean oil pan.
Install new oil pump & reassembly engine, WITH Magnetic drain plug and checking valve lash.
Spin the new oil pump with extension & drill to both test the operation of the oil pump & pre-prime engine.
Install distributor & with spark plugs removed, turn engine over.
Engine turns over fine with NO binding of distributor.
Reinstall spark plugs & start engine, run engine for 20 minutes at various rpms.
Remove magnetic drain plug & inspect for metal particles.
Drain oil through a fine mesh filter/panty hose ( ask Doug for a pair
).Remove oil filter & cut open, looking for metal particles.
If no metal particles are found, be HAPPY!!!
If metal particles are found, I would try to identify them.
Then install a new filter, reuse the strained oil, refill the engine & run engine another 20 minutes.
Repeat inspection process.
This time if there are metal particles found, I would then disassemble the engine, NO particles...I would think that ALL passage ways are NOW clear of particles due to the "Flushing Filtering" procedure...& BE HAPPY!!!...Mark