The 307 was a low end economy motor and the power pak heads were the performance option heads used on early 283s. I've seen power pak heads on other motors, so their presence is only telling you what the heads are, not the motor.

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...