The musical instrument shop was in Stockwell St I think, the record shop in the Gallowgate was a great Saturdays meeting place in the 50's and 60's. Survived into the eighties according to some of the guitar forums I found. If I remember correctly Golumbs(I am not sure this is the correct spelling)had above its door a leaded fanlight which read "Golumbs (sic) The house that value built". I got an acoustic guitar there for my birthday when i was about 13. I think it set my Mum and Dad back the princely sum of £14.
Hidden Glasgow Forum
I remember the store being on a corner, very close to the City of Glasgow Union elevated railway tracks. It stocked a vast array of parts, I believe...an aladin's cave.