WowoW,
I've asked the same question re my '67 GTV as it gets darn hot here as well. I must say while I was in HK I only saw two classics - one Mini Cooper and one VW beetle.
Both excellent examples and both turned a thousand heads as they stood out from the Toyota Crown taxis, but both are also quite bland compared to a 105.
So I can understand why your 1750 gets a lot of attention.
My Alfa mechanic here in Brisbane Australia has retro-fitted quite a few 105 coupes, spiders and sedans with air-con.
He considers it an easy conversion mechanically, but then he's a fully qualified mechanical engineer so I guess anything is easy.
Apparently the plastic encased condensor/heater box from Alfetta/Giulietta models is reasonably compatible with the steel encased heater boxes under the dash of a 105.
A couple of spacers or washers will be needed to get the box to sit correctly on the mounting bolts though, but otherwise the mountings are very similar.
On the downside you will probably have to reconfigure the air ducting, but this isn't that hard with some 50mm flexible plastic agri-pipe and some determination.
Under the bonnet (hood), it's all Alfa as well - recycling the brackets, pulleys and compressor from the later models.
The only question I haven't asked him is whether/how he adds an additional pulley for the A/C or if he just opts for a longer belt to drive the compressor as well as the alternator and fan.
Mounting the controls inside may prove a little tricky also, but it will be easier in a 1750 as you have a console to mount them on and to hide the new box.
In the 67 GTV there is no console, so things are left a little exposed.
Hope it helps.
Col
) His roundtail Spider had an aftermarket air conditioning unit, and I asked about it, since I had never seen one and thought it was a big deal... He explained that pretty much it was a requirement to have A/C on all cars due to the weather, and it was no big deal to have one over there. 
