66 C20 Air conditioning

[Calichevyv8]

I'm rebuilding my A/C system in my 66 C20. If you look at the top of the lid you can see some glue that was holding on some foam (which was disintegrated, you can see a bit of it on the top of the evaporater) and some type of gasket or seal around the perimeter. Anyone know where I can get this stuff? Didn't see it on old air which was the first place I checked.

Also, aside from getting actual new parts (rebuilt compressor, new drier, new resistors, tested evaporater, tested condenser, new hoses) what else should I do before taking it to be recharged with R12? I've saw some info about oiling the compressor and drier? I also saw a O-ring set but not sure what those are for. Thanks for the help, never messed with air conditioning before.