The duration figure is of course the amount of crankshaft degrees the valve is open for. Where the cam is degreed in at doesn't have any effect on that, it's ground into the cam. Advertised duration is a crapshoot at best because you don't know at what point of valve lift it was measured at. Some companies measure at .002", others could be .005" or even .010". That's why the duration at .050" of lift figure is used so you can better compare cams against a set standard of measurement.
Having said that many cam grinders will use chevy lobe profiles for all their cams which (because of the smaller diameter lifter) precludes taking advantage of the Mopar larger lifter diameter which allows for less duration at a given lobe lift.
As for dual pattern cams they are generally used to crutch a poor flowing exhaust port as with the old (and for what ever reason) much vaunted X and J heads. Newer offerings in aluminum and even cast iron heads both from Mopar and the aftermarket all have the better exhaust port patterned after the W2 so the dual pattern cam is not needed and would probably hurt performance and driveability.
