Ok, try this.
Unbolt the driver's side engine mount.
Use a bar or an engine hoist and see if you can move the engine to a position that clears the header tubes.
If the headers now clear, maybe you can shim between the motor mount and the K-Frame to get the clearance you need.
Your problem is engine location as there area number of members on here with the same setup as you with the same headers that had no fitment issues.
Cheers!!
Edit: I just noticed something else from your pics. That section of the K Frame that the motor mount sits on looks like its bent
downward. K-Frames are notorious for bad or cracked welds.
I wonder if this is your problem?