Ring and Pinion 373's

[roadrunner93]

A buddy of mine found a set of 373's at an auto salvage. When he went over to pick them up, they tried to sell them to him without the pinion. When he asked where it was, they said you can use the same pinion that is in the car now (He has 273's). I've never heard of that before, so he obviously didn't buy them.
Anyways, the salvage place called him back an hour later and said they found one. He thinks they are trying to rip him off. Are the pinions branded like the ring gear? How can you tell? Does the 273 pinion fit?