You will need to get the ends of the 16mm screws turned down to 12mm and partially threaded 1mm pitch.

Watch out, 12mm single row, angular contact bearings don't have dust shields, you will want to bury them in grease.

You can't use double row bearings with shields because they aren't crushable.

This is how I built up my Y screw assembly...

I put on one bearing
the aluminium mount that bolts to the machine
then another bearing
then a pair of Belleville washers
then the pulley
then a stepped iron sleeve to carry the indicator dial and the handle
then a 12mm half nut

I nipped in flat ended grub screws through the iron sleeve and pulley, flats cut on the screw shaft.

I wound the 12mm nut in one turn to preload the Bellevilles and crush the bearings.

Then I added another 12mm half nut to lock the first one.

Then I tightened the grub screws.

There was no need for a bearing at the far end of the Y screw, it simply isn't long enough to whip.