1250 and 1260 Oscillator Modules Interchangeable?

Does anyone know of a difference in these 2 oscillator modules? I have one of each and comparing side/side they appear identical. I know the difference in the Day/Date display on the 1260 but it that not just a function of the timing (drive) module? Omega does give them 2 different part numbers.

Any feedback from someone who has tried to swap them?

Thanks!
Michael