Well, hmmm, for one thing, Sean South was killed in the '50's, not during the Anglo-Irish (Black & Tan) war. Depending on the age of your "Glasgow Irish Catholic" (not Ranger supporters, I'd wager) they could have been contemporaries...

Silly song, never particularly liked it. Part of the "another martyr for Ireland" genre. Ah well, just my not so humble opinion.

Cheers -

Pete