If you are looking at two assembled engines; a 272 and a 292, the fastest way to tell them apart is by looking at the heads. The 272 head casting has clean rounded corners without any protrusions at the bottom front of the head, while the 292 heads have course casting mould breaks at the front and small protrusions at the bottom front closer to the exhaust side.
The exhaust manifolds on the 292 are larger than the 292 manifolds.
While the carburators appear to be the same, they are actually very different with a closer look. The '56 292 carb is higher CFM and has a larger throat than the little '55, 272 carb. In fact, the air cleaner off a 56, 292 wont fit properly on a '55, 272 and vice versa. Also the linkage is all different.
All the 56 292 engines had automatic choke, so there was a boss cast into the intake manifold for the heat riser tube. The '55, 272 intake does not have that. They were all manual choke.
If you were looking at a '55, 272 engine and a '57 or later 292 or 312, theres a lot more easily identifiable differences at just a glance to tell them apart, particularly the intake manifold. The old "bugsprayer" style carburator was discontinued after '56. A lower, wider carburator design debuted in '57 and remained practically unchanged thru the late 1970's. Along with it, a newer distributor design with mechanical advance counterweights replaced the old pre-57 Load-O-Matic distributor. The appear a lot different as the newer design has a much deeper distributor body than the Load-O-Matic.