Hi Fiona,
Good you got some news from Cydebank Library. I still have the feeling that Radnor Park is where your Grandfather was born, I'm sure that area was known as the Terraces. Could your GGrandma just have been friends with someone she met when she came up to Glasgow to live?... its another possibility.
I know you are going up to Glasgow on 16Th..its a long journey.. maybe I don't want you to get to disappointed looking for your streets. Renfield Street is much the same if you have the right number I'm sure you will see the shop you are looking for its right in the City centre. If I remember right..there is not much left of Shamrock street...there's one old building left but most of it is now flats. Its next to Stow college, I think it came under the district of Garnethill/Cowcaddens. Its just off junction 17 as you come into Glasgow if you are driving.. You could try google maps street level...you can view the street.