A 1200 crossmember has the bolt holes 656 mm apart. You may be able to redrill the holes as a 120Y is the same width as a 1200 even if the chassis rails are wider apart. I don't think anyone has done this before so if you can make it work it'll be a big help to 1200 owners.

Crossmember

My crossmember just needs the welding finished off and a tidy up.
Ive played around trying to fit and mod all those crossmembers your all discussing and at the end of it all i just modified original 1200 crossmember it keeps all steering and suspension in check.
At the end of the day there is no easier softer way if there was we would all do it.
If you can get your hands on a stock 1200 crossmember and you have motor and box there ready ill come and help you mock/weld it all up and you can do the rest. Good excuse to get away for a weekend and play with dattos.

Will you sell your crossmember? If yes can you put some photos up