Unfortunately, these speakers, as good as they were in those days, are really not very good. BIG SURPRISE to me when I opened my shop in 1974 and thought they were AMAZING until I put almost any other speaker next to them
Box speakers have come a LONG WAY since then, no disrespect to Mr. Kloss, so you might be better off buying (even used) a newer speaker than putting money into fixing those.
Cheers!