Is there much work in bending over the pinch weld. I have a RC 2 inch lift with leveling spacers and would love to run something wider like this. Do you need to run wheel spacers?
For pinch weld modification tips, check out this thread:
I've heard of a couple different ways. Most have used brute force and big hammers to bend it over. Others have used a sawzall and trimmed the excess metal away, although this method raised concerns of the resulting strength (or weakness, rather) of the trimmed weld. So, some have chosen to trim it, then add a weld of their own over the seam for reassurance.
After modding the pinch weld, you need to reshape the plastic wheel well liner to get the full benefits of the modification. A simple heat gun and some patience is typically all you need here, depending on how you want it to look afterward. Some have even decided to simply cut the plastic liners off, but that raised concerns of the coolant lines being exposed on the passenger side.
Personally, when I get around to it, I'm going to bend over the pinch weld with a BFH and the reshape the liner with a heat gun - seems to be the generally accepted method and retains the factory look as much as possible with the liners.
Regarding spacers, yes, I believe you will have to run spacers on the stock wheels in order to fit 265/70s due to the lack of clearance with the UCA bolt that hangs down. I would add them if you have a lift anyway, as it helps stabilize the body roll of a lifted XK with a higher center of gravity. You will notice a difference.