Why do my fenders fit so terribly?

[Russell]

Hey guys!

I'm in the process of re-installing my old fenders, and an old hood so I can shoot primer onto my truck without getting my engine / frame etc all covered with overspray. However, I'm having a lot of trouble trying to get my fenders to bolt up. Its like the cab is too close to the rad support, but I've got the rad support as far forwards as it goes, and the cab as far back as it goes.

Also, the back of my fender is looking terrible as far as alignment goes as well. There is a very small gap at the top, and a huge one at the bottom, leading me to think that the core support is up too high (put the fender down as far as it'll go on the core support, and I have like 3 shims up front, yet the physical body lines are not lining up at all.

Any ideas?