As far as I know, the U.S. (and Canada) didn't get any GTDs and no intercooled MK2s, an just n/a diesel and turbo-diesel (which was only available on the Jetta IIRC) and n/a gasoline engines... So anyone that has an intercooled diesel MK2 Golf (such as my car) were homebuilt customs or were brought over from Europe.
I also believe (but do your own research on this) that the brackets, pulleys, a/c pump and alternator from the gasoline engines will swap right over to the diesel and allow you to install a/c.
I do not know if the presence of the intercooler and it's piping will interfere with this or if the RHD dashboard will present a problem for the installation of a/c components.
I am also laughing a bit
and rolling my eyes a little
at your need for a/c in Scotland of all places whereas I don't have air con in my home or vehicles and it is going to be over 100 F (I think thats like 40 C) in a couple months.