I have just completed restoration on my 78 Salons heat/AC box. I purchased a new AC evaporator core and heater core at my local parts store. These parts do not come with new foam seals that slide onto the outlet ports to keep crap from getting in the box. I work in an auto accessories installation shop and some new parts have dense black foam squares glued inside the cardboard boxes. I worked in body shops too and replacement parts have these squares glued in the boxes too. So hit your local body shops and I'm sure they would give you some of these foam squares. If all else fails, buy a foam sanding block. What I used is 3/8" thick. I tried free cutting circles but they were choppy looking. What I found that worked awesome was a die grinder with a cone shaped rotary bit on low speed. It made very nice and smooth holes. If it was too small, I worked it a bit more with the rotary bit. To cut the main shapes I used a box cutter with a new blade. I cut them a hair big and shaped the sides with my angle grinder with a 36 grit roloc disk. This also made a very nice edge. Some others may have a different or better way so feel free to add to this thread.
