Although debatable, I think most would agree that the best production iron heads for a 302, that are reasonably priced and attainable are GT40 heads, and they're littered across any junk yard. You can pick them up cheap, lap the valves, put new seals on, and be running on a shoestring budget. If you have a little more time and money to play with, have them decked, put new springs on, and do some minor DIY porting and you'll have a great set of heads for $400 or so.