Joe, I have no idea if it will be a problem or not. Maybe Dean (Weeg) has a quick answer when he sees this. That's why I suggest you do a thorough job of measuring beforehand. Your 307 should be equipped with a short pump if it's factory original. The long pump, used from '69 on, is 1 3/8" longer. Doesn't sound like much, but it could make a difference. Preplanning will minimize chances of having to scramble later to figure out a solution to improper location (no personal shot intended there, just a reference). As an example, if you go for a long pump (serpentine or not), and you end up with insufficient clearance for a fan on the back of the radiator, you might make the compromise of putting an electric fan on the front of the radiator. Then, you could end up with a cooling problem that you spend all kinds of time and money on trying to solve.

Just giving you some things to think about.