identifying heads for 273

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.

64-65 used the 080, 315 castings
66-67 used the 178, 234, 920 castings 920 casting is the best
68-69 used a 675 open chamber casting