Just finished putting a Vintage Air system on a '70 Challenger big block (with original A/C equipment under the dash). The stuff is very nice and works very well, but do not assume that their dimensions are accurate for drilling holes and the like. You'll have to test fit everything. I did the under-dash part when the dash and seats were out, so it was more comfortable and easier to see what I was doing.
We had the A/C style blower hole in the firewall that they provide a block-off plate for. The plate also has holes for the four tubes to go through. For example, if you were to bolt the plate in using their placement, two of the tubes would interfere with the edge of the firewall hole. Also, the sheet metal brackets that hold the heater box on needed tweaking to make the box sit square (then the recommended spacing for their hole locations are off). Long story short: it's not plug-n-play.
The tubing in the engine compartment is routed nicely (except some don't like the tubes going OVER the radiator support by the washer bottle. They provide another alternator support bracket to use, but we used the original. The hoses to and from the compressor need to be brought to a hose company and have the ends crimped on in the correct directions.
If you go with Vintage and you have a big block car, I'll be glad to take pictures and offer real-world advice on the install.
