Swapping Second hand from new 21j to ETA on SOSF?

[Vigil]

I have the new style (arrow) second hand from a 21j that came from T4D and I have a
Swiss ETA with a "block" second hand on its way. I just want to swap second hands, should that be a direct swap or are the mounts completely different?

 

[fakemaster]

They are different

 

[Vigil]

Thanks, that saves me a tear down session