With a 350 Olds in place of your 307 and dressed with everything from your 307 , I doubt this would ever happen and even if someone noticed the swap they would most likely compliment you for adding some much needed power under the hood of a great looking car and for going through the effort to make it look factory and keeping it Olds powered.
The only possible issue is someone trying to get passed smog check someplace strict like CA and the inspector notices the wrong block casting number Through even in CA most inspectors don't look that hard. The Federal law is you can't swap in an engine older than the car itself, must be same year or newer. So legally speaking this precludes larger Olds engine swaps as they predate most G bodies.