Wider tires on skirted Caprice

What is the widest tire i can have on a skirted caprice, i have 225, but i would like to have 245 in the rear and 235 in the front. But the dang skirt in the back doesn't give me any room at all for wider tires. Do i need to get a shorter rear axle or extensive remodeling in the rear wheel tubs?
Any help would be nice? Even if its just an idea.

Have you fooled with bigger wheels/tires yet?  I see your post is from july. 
 
If so, what did you come up with?
 
If not... I have been doing some preliminary measurements on my '82 wagon and it seems like the front tire width and wheel backspacing is my only hurdle.  I figure I can go with a 255/45/18 tire on an 8.5 inch wheel with stock backspacing.  I do not know stock backspacing and have to measure that next. 
 
Something else I do not know is whether the tire will rub the outer lip of the front fender with suspension compressed.  Rear tire clearance is no problem at all with this size. 
 
the tire section width for a couple different brands on a 255 tire is about 10.4 inches and that is what I'm basing this all on. 
 
Thanks