First attatch the inner fenders to the body where they're supposed to go.
Then do what it takes to put the core support where it needs to be in order to fasten to the inner fenders.
What about the fenders? do they bolt up as they're supposed to? Is there per chance, an extra set of holes in the frame for the body mounts? (I kinda doubt it)
All this is assuming that you've not modified the frame other than replacing the old crossmember and front suspension, with the newer stuff.
Try your origional core support, They may have gotten the aftermarket one wrong. (not that it's ever happened before