I ended up buy a junkyard support of the normal "third" bench seat, cutting in half, a front seat with swivel, welding the swivel to it, and viola.

I was pretty easy to find, straightfoward as the support for the bench seat, can be neatly cut in half with a saw.

For secure seat belts you have to bolt them on the support (not the seat).  I have two sets, one for facing forward, one for facing backward.