identifying heads for 273

My question is if I use anything but the stock heads, externally do they look the same?

On a 66 or later engine you probably wouldn't be able to easily tell which heads are on it from the outside. So, yes, they will look the same.

On your 65 engine, since the bolts that hold the intake manifold on are smaller in diameter (IIRC) & are at a different angle than the 66 & newer engines, it would be easy for a knowledgeable person to tell the heads had been switched. Most people would never spot the difference.