12'' wide rally wheels.....

[nxtlevl]

I found a pair of truck rally wheels that had been widened to 12"....the guy told me the offset was enough that the rearend wouldn't need to be shortened, but I was wondering if I was going to run into any other type of clearance issues.....was thinking about a 315 series tire, but wasn't too sure...Hopefully it would fit without any major modifications..
My '87 GMC is lowered approx. 3''...(looks to be just a shackle flip)....so I would think it should be alright....I just bought this truck last week, and have been trying to gather up parts for a re-do next year....Any input would be greatly appreciated...Thanks!-------------Ed