I think 107-110 with 35-40 inch tires would be ideal. The obvious problem is the bed, you can either ditch it or bob (shorten) the front. The next problem is the gas tank; mine is the smaller 16 gallon and I could probably move the rear axle forward 3-4 inches before it would possibly hit the gas tank. You could use a fuel cell or use an XJ tank behind the rear axle like XJs have them. The curve of the frame might offer some complications; If I moved my rear axle more than 10 or 12 inches forward there wouldn't be much room at all before the axle would hit the frame on compression. LIke you said, just make new spring/shackle mounts, and shock mounts, pretty straight forward if you can weld. For a driveline, a shortbed driveshaft would only get you in the 113" range, a 2wd XJ shaft might be a good length. If you're over 110w.b. you can probably go to 8 inches without an SYE, if you're 105-110 you can probably go to 6 inches, either way you'll want a YJ yoke (cheap).