All of the photos of River Boat on the IPDB show reverse wedgeheads. Look at the distance between the top edge of the glass to the outside edge of the head compared to the bottom edge of the glass.

Strictly a reverse-wedgehead game.

The first Williams reverse wedgehead game "Trade Winds" is the only one that can be found with a rectangular head. The sales flyer shows it that way, so obviously they were the early production ones. The only other variation that I've seen in the series is two different paint schemes on the head of "Heat Wave".

also ten spot came in two different cabinets. Actually it was going to be a styling of the sixties cabinet seen in their promo flyer and ended up being the cabinet they used up to the reverse wedgeheads. that head you have now might be pre reverse wedgie from a machine like ten spot or reserve... etc

Going back another generation, "Darts" came in both woodrail and "styling of the sixties" cabinets. The woodrail version is much less common.