PK3LC 1976 Indonesia
PK3 counted as a seperate DXCC entity, Java, until May 1, 1963. It then became part of Indonesia. It is strange to see a PK3 prefix being used in 1976!
I didn't find anything about him having had a YB call. He became PA0CLC (CLC - Clem le Cotey). I haven't been able to determine when PA0CLC was issued, but QSOs with PA0CLC start in Club Log in May 1976 (one QSO, before Patrick's PK3LC QSL) and then late July 1976 onwards (after Patrick's QSL). So it does seem as though he may have moved to PA-land in mid 1976, perhaps when he retired? I didn't find anything about him being QRV friom Indonesia after the 1950s.
Patrick Rigg Collection
Info courtesy of G4UZN