Before I ripped the strombergs off and replaced them with the triple su's . I restored my 70 cleaner as well.
If I recall mine was off of a 69 oldsmobile air cleaner......
Its a vaccum flap. standard in the industry at that time, call NDP,CLASSIC RESTORATION PARTS. Any of those reproduce everything from the muscle car era.
For your own sake if you just cap the hose, it will stay open all the time. Just make sure it isn't rusted closed.
Good luck.
