The Saginaw box used on the XJ is metric, therefore I would think the bolts are as well. I don't remember if I measured them last time I had them out, but I would imagine either M10x1.5 or 7/16"-14, with a length up around 3".
What happened - did you lose one? Just wondering...
5-90
EDIT - BTW, I could be off on the length, after reflection. I'm pretty sure about the size, tho.
5-90