Blaster,
I'm piecing my a/c system back together as well. The only parts I didn't change out are the evaporator and the expansion valve and, of course, the evaporator had a leak. I ordered new ones from "Classic Muscle" in South Carolina. The evaporator was 260 + shipping. They had it in stock and it shipped out the next day.
I received it yesterday and it looks pretty good. I'll be installing it this weekend. I'll let you know if there are any problems.
http://www.oldmusclecars.com/
Kind of hard to navigate their site but click on "Chevelles", then "Order Parts", then enter part number 3016987 and click "Search" It will show you a photo of the part.
It didn't come with o-rings so you'll have to order some or get them at the parts store.