Rim exchange
#1
#2
Short answer is yes, they have the same bolt pattern and hub size. One thing to check is whether the lug nuts are different; I have a spare set of wheels from an XK8, which is based on the XJS, and they use a completely different set of lug nuts that require a different wrench (21mm flat for the XK8 vs. 19mm tapered for the XJR). Your XJ6 might not have this problem though, but always good to check.