Ok, this is fast.

But it is not definitive.

The question is whether the u-joint will slide onto the new rack's shaft.

I don't know, but if it will, then the unsplined part of shaft has to slide into the split in the U-joint. If that is the case, then I would expect to find the unsplined section crossing the "machined horizontal slot" at that slot's middle-point, and I would expect that only one (or at most two) splines are missing from the shaft.

The other possibility is that there is a machined "vertical" groove in the u-joint, apart from the split. At this point in your disassembly, I think you can simply look to see if that is true.

In either case, of course, IF you can conveniently remove the U-joint from the intermediate shaft, you can make a definitive fit-check off the car. But the U-joint may well be essentially welded to the intermediate shaft by dissimilar-metal corrosion.

If worst comes to worst, you could grind down the unsplined part of the shaft (dremel work?) until things go together nicely.

If you get that far, using never-seize on the aluminum-u-joint/steel-shaft connection might help reduce future corrosion problems.

I feel for you. Good luck.
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jds