Need help lining up fender

[Tri5Nerd]

I'm just getting back to working on the 55 and lining up the passanger fender is driving me crazy. These are not the original fenders, they are from a 57 but they should line properly, right?

I had to make some brackets on the cab to bolt the fender on since they were missing from when I got the cab.

Please take a look at the pictures and help me out with this one. When I try pushing the front of the fender to the core support the area where the fender is bolted to the cab moves and the gap between the fender and the cab opens up.

The drivers side fits perfectly without applying force.