Mark,
The 383-2 and the 383-4 (330hp) both shared the same cam & head assembly. the 383-4(335 hp) use the 440 cam & head assembly. Both 383-4's used the same carb specs, whether it was a Holley or a Carter; the only difference is for auto/manual trans or a/c vs non a/c.
Cam Spec's [Std versus HP]:
Intake Open (BTC): 18 deg versus 21 deg
Intake Close (ABC): 58 deg versus 67 deg
Intake Duration: 256 deg versus 268 deg
Exhaust Open: (BBC): 66 deg versus 79 deg
Exhaust Close (ATC): 14 deg versus 25 deg
Exhaust Duration: 260 deg versus 284 deg
Lift: 0.425 versus 0.450
All of the piston specs, etc are the same between the two. However, the spring rates were different on the Magnum Heads:
http://vintage.mitchell1.com/PClubData/chassis/den73/V2D735033.pdf