That's how I understand it too, you can mix the two and I use the ratios interchangeably. 3.07 is technically what I have in the rear of what I'm looking to convert.
I'm interested in that XJ either way. It seems there are a few things out that direction I need to check out.
This is for a 2wd conversion I plan to sell after its fixed/converted so I'm hoping to find something closer as the drive cuts into costs. If it was for a keeper I would't mind the drive as much (like for the MJ door skins/seats out your way)