64 bed problem

[Raked 64]

Hey guys,
New here, but have been building my 64 for a long time. I am almost done with a frame off restoration. I have hit a few snags during reassembly.

I have a 1964 short bed fleetside. Here is my issue. I bought a fleetside short bed from a 1962 0r 63 and I painted it etc. Now when I go to test fit the bed, the mounting pads dont line up with the 64 frame. I can drill out the spot welds and try to modify the pad locations?

Or am I better to buy new cross sills?

Are the holes in the front of the bed going to line up with the wood for a 64?
I need to figure out a plan to remedy this situation.

Thanks for any help.