I've sunk a ton of money into refurbing my original a/c in my 73 and although we finally solved the lack of airflow (stuck trap door) it still doesn't blow anywhere near as cold as my late model pickup does. The shop that did the work basically has said that's as good as these old systems would do. Not sure I've totally resigned myself to that and may take it to another shop for a second opinion, but the shop I work with has been dead on about everything else they've worked on family car wise. They are also a Vintage Air dealer and now are saying that if I want it any cooler thats my next route. The compressors are modern, operate at higher presssures, have larger more efficient condensers, etc. The only thing is they told me it would be between $3 - $4K installed and that the kit itself was right at $2k. I've looked on Ebay and found what I believe to be the kit I would need and it was closer to $1200, so I'm wondering if they are thinking about the more extensive & expensive kit a car originally without a/c would use. If you read enough car magazines you'll notice most of the high dollar cars use these systems so I have to believe properly installed they're as good as you're going to find. Good luck and let us know how it works out. I may be doing the same at some point myself.
Later, Jim