I'd get it in the vehicle, trans mounted, then loosen the fasteners everywhere, and shift the motor/trans as mentioned in many previous posts, - before I put a single ding in the header.
Good luck.
There is a lot of movement possible when all the bolts are loose. Forward, backward, right and left. I wonder if those headers were actually made for power steering? Regardless, it looks like you're really close now. I think you can do it. Good luck. An extra helping hand might help also.
I also had a fellow remind me that the k-frame and trans xmember don't live on the same plane as they will after it's in the car. Things are gonna change at that point.
The bolts between the mount bracket and the block are loose, and all the mount studs are tight right now. I forgot about that too.
Yes these headers are made for power steering. I bet once I've got it all in the car it puts the tube right into that curve in the steering gear.