Base cal. 321 balance snafu. Possible transplant?

I sent a cal. 321 Speedmaster to my local watchmaker because of timing issues. He found that the collet on the balance was broken. He said these can be replaced, though he was too old to do a good job with that.

So I suggested we use a balance 321 balance complete I had in my parts bin.

He got the balance and said it was a Lemania, not an Omega, and that it wouldn’t work, because it had a “D” shaped stud, instead of the original triangular one.

Questions: is a collet easy to replace on an original 321 balance? Could I use the Lemania balance if the stud was changed…and can it be changed? Which of the two options (changing the collet, or the stud) makes the most sense, and has the least chance of a major problem? Many thanks.

Looking at the two jobs in isolation, changing the stud is easier than changing the collet.

If the new balance will work or not depends on what the final length of the balance spring will be after changing the stud. If it’s close to being the same as the original, it should be able to be made to work.

Changing the collet would eliminate this question...

So whoever is going to do the work will have to look at it and decide what the best option is.

Thanks, helps a lot.

A follow-up: I found this 321 balance without the hairspring, but it has the collet and jewel. The original balance has the broken collet, that was glued back with crystal cement.

Is it possible to remove the hairspring and stud from the original balance, and fit it to the replacement balance pictured? Very difficult?

It's not difficult at all,. but likely there will be some adjusting that needs to be done after.

Thanks