The tartan is not clear and the glengarry was shared by most Highland regiments. The hose and sporrans may have differed among regiments but I am having a hard time nailing down exactly which aspects would be indicative.
However, I would punt a guess at the Argyll & Sutherland Highlanders - despite the name, their recruiting area included Stirling and Falkirk, with the depot at Stirling and TA companies in both. So they seem the likely candidate on geographic grounds. In addition, the Argyll badge broadly fits the shape of the one in the picture (roughly circular with a little point at the top).
Edit: a different event, but this page has pictures from the Argylls mounting guard at Balmoral in 1962, and this photo is from an inspection at Catterick in 1978; the uniforms are a good match for what we see here including the hose, badge and sporran).
Given the spectators are looping around behind the soldiers,they're sat quite close, and that they're not on a parade ground, I would guess this is perhaps not a full-scale military event like these
Two points that might help date it but I can't draw a direct conclusion from them - firstly, it's hard to tell from the angle but I think they are carrying older style rifles (no box magazines like in the 1962/78 photos), which may lean towards it being early. Secondly, only one of the men is wearing any medals - no widespread campaign medals.
