So I have my 97 XJR Chrome wheels on my 98 and they look great. I feel I need some wider tires, especially in the back since this car has no problem tearing up the tread. I've been told they are 17x8 and that I could run as wide as 275s on them but the problem I worry about is clearance. Anyone running that wide of a tire?

 

First of all, I should not fit 275 on a 8J rim.
Yes, it can be squeezed on, but the rim is too small for that size tire, and the tire will deform, which can/will result in some nasty consequenses.
A 245 or 255 tire will fit the rim though, and is a pretty standard width.

Having said that, yes, 275 will fit, I have them on the rear, albeit on 18x9J rims.
The wheel well is spacious enough, with only the bump-stop obstructing, depending the exact tire size, rim size, rim offset, and even tire profile.
In my case I 'halved' these stops, allowing for a 1/4 inch spacing.
Half hour work max.