Can 305 sbc heads be used on a 350 engine?whats the good bad and ugly of it?

Depending on the 305 heads, yes you can. If you get the right ones they'll give you greater compression but you'll still be able to run on pump gas. Check the casting numbers first though because I am pretty sure the ones you want are the 14014416 casting. You will also get good bottom end and mid but in the highs it wont be as good.