[mepstein]

I'm still waiting on my car to get painted - It's been forever - but I did work out the installation in my '67. Like Jonny said, you have to remove the cowl stay and make a path for the entry and exit from the cabin to the evaporator under the cowl but the general install is similar to the later cars (we've done a bunch at my shop). I'll close off the fresh air opening so it's 100% recirculated air. If I need fresh air, I'll crack a window. I've also used lizard skin insulation and ceramic coating on the underside of the roof, floor pans, doors and in the engine compartment to keep heat out and a/c in. Glass will get a light colored ceramic film to keep the suns rays at bay.
But overall, the difference between a SWB car and later is really just some adjustments to mounting the evaporator and plumbing the inlets/outlets. I'm actually happy that it doesn't have the cowl air distribution boxes of the later cars. They just slow down the air velocity.

I'm also putting the system in my 914 with a 3.2 In that car, the evaporator box doesn't fit under the cowl so I'll use an under dash unit.

For me, it's worth spending the money. It's hot and humid where I live and a/c just makes the car more enjoyable to me on more occasions. I drove a 914 as a daily driver for 8 years when I was younger but parked it when too many hot humid rainy days just made driving it a miserable experience.