The new, additional fan neded a specific ventilation box custom made and fitted in the bulkhead.
With these modifications, it is now possible to use both A/C and heating. I do not feel that I have depreciated the car's originality with them, as they could well have been performed on a new car; and indeed, I had fitted a secondary A/C unit on my brand new 604 GTI when I had bought it new in 1985.
Lastly, the ignition has been replaced by an electronic one from a Volvo. Tim also pressed me to "upgrade" to fuel injection, but I perceived this as taking too much originality away from my car.
I have test-driven my "new" 604 for over 3000 miles. It runs beautifully and idles smoothly - even with all fans and A/C at full speed. The most striking is the increase in power and nervosity - the car just wants to accelerate and accelerate, and all of this seems to take very little effort.
My 604 is now probably the world's nicest. Anyone can deny this?