Longines movements: is it possible to swap calibers 13.33 and 12.68?

It would seem to me that it would depend on the case. I have a Longines 12.xx and 13.xx on my bench right now. Considering the case I want to use, there is no conceivable way the bigger movement would fit.

The picture shows a Longines calibre 13.98 on the left, and a Longines calibre 12.92 on the right. Your initial question was regarding fitting one movement into the other case. I’m not saying it is not possible, because sometimes people fool us. But fitting the 13.xx movement into a 12.xx case would be a challenge I wouldn’t undertake, fitting the 12.xx movement into the 13.xx case on the other hand, might be possible with a special adaptor ring machined with the right i/d and o/d dimensions. Let us know how you do.