I/O Box Seat; What hardware was used here

[BigLew]

You might be able to find something like that on either the TODD or Garelic websites. They do a lot of leaning posts, seats, etc.

Another thing you might consider is putting a padded "leaning board" across the transom coaming arch and then have a cushion made for the top of the engine box attached with snaps along the edges. I have that on mine and it works out reasonably well for younger folks, or the young at heart!