Bob, you pretty much hit on all of the differences, the door panel armrest is built into the bel air where the 210 has a hand opening pull, that is a dead giveaway When someone is trying to pass a 210 as a bel air. The speaker has bel air where the 210 is blank, I’ve owned a lot of 55 Chevy's and there are probably more differences then I could think of. I just sold a bel air and I have a 210 in the garage. The side trim is the most visible.

Richard