You have to remember cam choice is not really a function of engine displacement as it is compression ratio.
Pontiac engines, being that the vast majority of them were made after '71, are severely detuned smog motors and later in the '70's had an abysmal compression somewhere around 8:1 or 7.5:1. So, cam choice has to be conservative in contrast. The heads flow similar to the average Chevy iron head.
I would say the average mildly built chevy has around 9.5:1 compression, so adjust the duration figures accordingly. Compression ratio and cam are fundementally related, as cylinder pressure is what actual makes power.