The Incabloc is the shock setting that is installed on the balance c0ck and on the mainplate of the movement.
Each Incabloc hold a jewel assembly supported by a spring to prevent damage to the balance wheel pivots due to shock, bumps, etc.
On the asian rep movements, the Incabloc looks like this. Both openings for the spring are straight sides and shaped somewhat like an "I".
REPLICA movement INCABLOC
The Genuine Panerai movement on the other hand looks like this, it's got one end that is straight sided, but the other end is curved...
GENUINE movement INCABLOC
A closer look at the balance c0ck and you will see the detail of the modified jewel setting.
GENUINE CLOSE UP
I have circled the section that is different on the genuine Panerai movement, you see how the straight sides have been cut away and curved. I don't know who came up with the term "Y", but if you note the shape of the attachment for the spring assembly, it does somewhat look like a "Y".
MODIFICATION
Here is a standard replica movement, AFTER I modified the Incabloc setting to look like the genuine setting. The work involved requires that the spring and jewel be removed, then the balance wheel is removed, then the setting is pressed out from the balance c0ck, the "Y" is created by hand, it's cleaned up, then re-assembled, balance adjusted, etc.
So there you have it, the "Y Incabloc" modification is nothing more than reshaping the Incabloc setting to match the type of setting used on the genuine Panerai's...now you know.
Thanks for reading.