I finally took the chain in for appraisal and the jewellers were in awe. They did acid testing on the clasp, chain and crucifix and it all offially checked out as 18k.
Since the bell (hanger) was the only part stamped, there was a tiny inkling of doubt. Now that the doubt is erased, it feels great that it's validated.
While there, I sold some broken 925 hoop earrings and some junk silver and used that to treat me and my youngest daughter at Braum's for ice cream.
It was a good day.