According to my parts book, that welch / core /freeze plug [pick one] is called a "taper plug" & it goes by the part number 00933-15000 for the 50mm one & 11019-32200 for the 44mm one. One of these is the one for the cam bore, but i do not know which one.
If you hoist the engine out to replace this plug, then replace them all,.... with brass ones. I think Repco still list these as a kit.


While you have them all out, give the coolant galleries a bit of a clean out with a suitable screwdriver & a hose. No point in doing half a job.

1200RC
You were right