Just for clarity, are you saying you can get the left side of the header on but the right side of the header you can't align to install the bolts?
Just want to make sure we are talking about the same thing.
As Elbert said, a crowbar is what you need to spread the header open enough to align it up correctly. Even on your back on the ground, you should be able to do this.
How is the car supported?
- Up on car ramps?
- Up on blocks?
- Up on jack stands?
- Sitting on the ground?
Rhino Ramps give a fair amount of clearance underneath.