I just had a quick measure to check. My 1974 (early) 120Y lca are the same length as the girlock stanza lca - about 308mm from centre of balljoint to centre of lca pivot. But they are definitely not identical in every way. the position of the sway bar link pin, and the bolt spacing for the castor rod are different. I didn't check the bolt spacing for the balljoint, and I didn't have any 1200 lca's to measure.

Another interesting thing is the 120Y steering arms are 15mm shorter then the stanza's, which means you'll have slightly faster steering with the 120Y arms.