The most effective one is the under dash one, but it looks ugly and sticks out like a sore thumb.
I'm using a standard WB heater box (as it has the centre face vents).
Possibly looking at putting firewall fittings on. (Like this one http://speedyairspares.com.au/produc...g-162-174.html)
Small aftermarket compressor as hidden as possible.
Run A/C hoses along chassis rail so it can hardly be seen.

HOPEFULLY this way it'll still look very standard but i'll have nice cold air con. :D