Doubt it very much is a republican arms cache.
Not in that part of Glasgow anyway , too near Drumchapel which is a majority 'Loyalist' area.
Bearsden area is quite affluent , I'm talking swimming pools in the back garden for a lot of it...So a very unlikely place to find these weapons.
SA80 could be one that has been 'misplaced' in Ulster or on operations in Afghan or Iraq , doubt its a frankenstein build , you simply do not fling away parts of assault weapons , not British Army ones anyway , they get lost - complete , or they get handed back to the arms kote - complete.
I suspect that the SA80 in question could be an army cadet model which will be easier to obtain than a regular forces one.
Kalashnikovs ? probably 10 a penny in Glasgow

,Handguns ? take yer pick...
Probably belonged to one of the Glasgow crime gangs.
Now if grenades and explosives were also found I'd suspect terrorist involvement , but for those weapons - criminals I think.