repairing front frame rails 65 cuda

I'm planning on how I'm gonna go about repairing my frame rails on my 65 Cuda. The bottom of the frames rails are gone from about 4" behind the K Frame to almost the torsion cross member. I'm worried about making sure there repair straight.

So my thinking is from the rockers make sure the car is level Front to back and side to side and to measure from the holes in the frame to make sure there straight left and right. So my question should the front frame rails be level or is there an angle to them ?