The steering box ratio in 1000's & 1200's is 15 to 1 while the 120Y & Sunny [B310] ratio is 16.4 to 1, so I presume that the helix on the worm is different.

I have no idea if the tooth angle on the ball nut & sector is different, but the 1200 uses a steering column as part of the worm while the 120Y & Sunny use a short splined shaft that has a fabric type universal joint on it.

This means that even if you can get a 120Y worm [complete with matching ball nut] into the 1200 steering box, you still need to change the column to one that connects up with this universal joint.
If this looks like being a workable solution, then you would also need the top cover from the 120Y steering box too. [where the worm shaft comes through]

I've not compared the 1200 & 120Y steering boxes, but I suspect that the steering box housings will not interchange between the two chassis.

Perhaps somebidy can confirm or refute this.