For my my 1977 I purchased from OReilly Auto, part number 603-001 Universal Recovery Tank made by Dorman. It had a tubing nipple on the bottom which I had to drill out for the hose to the radiator. I then mounted it to the plate where the original one was mounted behind the front access cover. The tank came with cap that sealed and would not vent. However in the “Help” section was a vented cap that fit the tank. Except for the capacity being slightly less than the original from Chevy, the replacement has worked just fine. The price locally for the tank is $9.95.
Good luck!
This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.