GM had some problems with that system and they stopped using it. I don't know the inside scoop on the engineering reasons why they stopped using it but they did.

The trapped air is the main problem and maybe that air bleed is all that is necessary. Then again, maybe they spent a bunch of time shaping the water jackets inside the heads to promote the flow of air and water?

On a Mopar engine that was designed 50 years ago it seems a little too odd that a person could just change the direction of the coolant flow and not have any negative effects. Maybe there is some happy accident in the design that allows it to work that way?

I've run the reverse flow setup on the dyno and haven't seen any problems but that doesn't mean the problem isn't there. We don't have this engine equipped with any type of multi-channel data logger hooked to thermocouples buried in the heads. So who knows, the exhaust valve on the #5 cylinder might be ready to melt and we wouldn't know it until too late.

I've seen a few SB circle track motors that run reverse cooling and those motors tend to use external water lines and tricks like that to get the temps all balanced out. I've never invested the time to do any of those tricks. Once again, on the dyno it might not matter too much. The cooling tower is higher than the engine so air is going to get bled out of the system in the tower, and we have an huge supply of cold water flowing into the tower so cooling isn't really a big issue.