The stock 305 came with 58 or 61 cc combustion chambers in the heads and had deeply dished pistons. The 350's pistons are not as deeply dished and they came with heads with chambers of 62, 72, or 76 cc's. So, if somebody just bolted a set of large-chamber 350 heads on that 305 without changing the pistons, the compression ratio will actually be lower than stock and it will be a real dog.

I have never heard of a 305 being "snappier" than a 350. They have the same 3.48" stroke, so the rpm range is similar for both engines. Remember the old axiom: There ain't no replacement for displacement! Take the 350; it will make you happier to start with and you can do more with it.