I can add a little to this. I have a GTD which had a low spec a/c unit installed. Useless, it was! So I designed an upgrade for it, and obtained additional parts (condensers, hoses, unions) from FenAir at Kings Lyne, and had the whole thing recharged with a local compny in Scotland, where I live. Be careful about the refrigerant. If yours is a new build, then R134 is OK. But if you are doing a rebuild on a system that had R12, beware. The refrigerant oils used with these two gases are quite different, and are NOT (repeat NOT) mixable, despite what some refrigerant engineers might say. Something one gets used to with a GT40 is that distance ceases to be an issue, you just have to go where the parts or services are.
Stay cool (says he, -5 outside today!)
Peter