That's what I loved about the older Ocean City's benches. They were reverable just by moving the back of the bech forward and backward so you can people watch on the boardwalk and people watch on the beach.
They have been mostly replaced by the following:
It seems to be that you can modify a few bech plans to make it work. For instance:

Shortening the light green support and putting in a left support leg like the right one. would allow toy to put a movable back that can be tilted frontward or backward.
Google bench plans to get some more ideas.