Dan,
Wasn't the "C-Body" 383 4-BBL, NOT technically an HP engine; but a 383 4BBL engines with HP manifolds, dual snorkel and dual exhaust? 330 HP vs. 335 HP.
In the C-Body world, the 383 4BBL with the HP manifolds, dual snorkel air cleaner and dual exhaust from the factory is our "383 HP" engine package. The alt, was "lo-po" 383 2bbl 290 horse. Correct?
Everything but the cam was the same on the 383 4BBL 330 horse vs. the 383 HP 4bbl 335 horse,....correct? Just 5 HP difference.
Or wrong-O- ?
I know you addressed Dan but...
In the C body world, the C body 330 horse is incorrectly called the HP. From 68-70, there is a specific variant of the 383-4 bbl used in A, B and E (1970) cars that contains different parts and is considered the HP version. There is no 335 horse HP C body assembly.
There is no such thing as HP manifolds. There are 2-bbl and 4-bbl manifolds.
The 383-2, 383-4 330 horse and 440-4 350 horse all used the same cam. The 335 horse and 440-375 horse used the same cam and associated valve train.