Hi AcemanToo
Although repairing Jaguars was my business for 20+ years I can’t say I ever looked at the Ace front suspension and thought those ball joints look like Jaguar, but that maybe because I’ve always been deeply involved fixing other things when working on the suspension!! But aren’t they Ford Mondeo/Sierra or similar?
Thinking about it I don’t think they are Jaguar, but that doesn’t mean they can’t be adapted. The distance (pitch) between the two mounting bolts is the critical measurement (the ball joint width could be adjusted either by machining or shimming). Pitch according to XJ6 workshop manual is 1.75 inches (44.5mm). (Wonderful things old time Jag manuals – gave all possible info necessary to fix the cars. Not like modern manuals that give away nothing of use!!). The bolts are 3/8 diameter (10mm), whereas from memory Ace joint uses 12mm (1/2 inch) bolts. This could be overcome by boring out holes joints to 12mm or inserts in wishbones or machining up bolts and nuts with shoulders.
Hope this helps.
P.S. I do have a Daimler Double Six sitting in the garage alongside Ace, but getting wheel off for detailed comparison would be a lot of hassle (too much junk in the way!!).
Let me know if distance between bolts is same (1.75 inches).