The biggest problem with the 337 was that the matching cylinder heads were never released. The 337 is designed to work with a standard height MW head and those don't exist anymore. All of the aftermarket MW heads use a raised port.
440Source use to offer a MW version of the Stealth and those heads on an RB block would be a perfect match for the 337, but those heads are a slow seller and they might not even exist anymore. If anyone was going to sell the 337 it would be 440Source since it would work with their heads. If they bought the tooling it might make a cool combination. Basically a "factory" version of a single carb MW engine.

I think the 337 was designed to work with an aluminum version of the original MW heads. That combination would be perfect on an RB block but Mopar Performance never released an aluminum MW head that I know of. Or if they did introduce one the killed it quickly.

The built in valley tray in the 337 just adds weight and complexity when you use it with Indy -1 heads or the Edelbrock Victor heads. And I doubt that anyone really wants to spend money to develop a standard height MW head when the raised port heads work so much better. So on one hand, the analysis was correct, it was a low volume product so maybe it should've been killed. The more complex story is why was it ever created in the first place? My guess is that something went wrong. Maybe it was supposed to be part of a bigger package of parts and the bigger package didn't get approved. The cast in bosses are a clue to some future that never happened.