Rust is in the usual places, but you also need to check down the A pillar. Open the bonnet and look down. If you can see sunlight (or take a torch), don't touch. Check the battery area under the rear seat, and the heater channels (exactly like a Beetle's).
Seals in the rear boot are important to keep fumes out of the main cabin - make sure the engine lid is properly retained and has a good seal. Talking about seals, check out for oil drips etc.
For an early notch, I don't think you've got dual carbies like later ones, so there should be few problems with tuning the engine properly.
Early notches had more in common with early beetles, whereas later Beetles adopted many of the Type 3's nice bits like disk brakes, fuel injection, semi auto gearbox, etc.
I'm not an early Type 3 person by any stretch. Hopefully one of the breeders will come and post.
Check out
http://www.vwtype3.org/
Lots of cool info there.
Andrew