There was a discussion on the other forum about two air filters (one from a 1320 and one from HC), and if I remember right their flow ratings were measured at 2 in of H2O.
Scurries off to check...
Yup, 2 inches of water. Keep in mind these are in a low vacuum environment. However, if you wanted be really accurate you would put a pressure transducer in line (pre-throttle body) to see what the actual operating "pressure" is from idle to redline, and then choose some key datum points along that curve to test each intake. This is pretty easily achieved in HP Tuners.
The next thing you should consider, which I am sure you have, is the actual flow rate as installed in the car. The measured/calculated air mass is a huge tell in a real world application. The best bet would be to baseline the car with the stock intake in place and determine where your air flow error (commanded power enrichment (PE) vs PE Error) stands. Then add each intake in succession, resetting the Short and Long Term Fuel Trims between intakes. You'll probably need upwards of three passes on each intake for the ECM to learn and adjust. Again my experience with the compensatory rates in the Dodge software is NIL at this stage (still waiting on my car). But, that is the theory.
The last thing I would offer is flowing a 4" tube with a bellmouth/velocity stack on the end.