Shep
I've done it to my RS using factory bits from donor cars. I only found these bits in Ghia's (ie: haven't seen an RS with factory air)
The glovebox is gone - this is replaced by factory dash undertray that incorporates existing swiches/ashtray etc
2 Biggest headaches I had were looking to fit the compressor as I'd put Twin DCOE's on & there wasn't room for any compressor - got something small from a diahatsu or similar. I have just run the hoses out through the existing hole in the firewall and didn't cut it to accomodate the factory connections that would normally run copper pipes etc running to receiver dryer. I did have to drill 4 holes in the radiator support panel so the condensor would sit up front - everything else is just a case of my Air con guy putting connections on rubber hoses and routing where appropriate.