You don't have to do either. It's easier to pull a motor in some cases or drop the K in others, but some header designs install with the steering shaft going through the driver side. Therefore it still must be installed with the engine in the car. Prepare for lots of cut/bruised hands and cussing but it's completely doable.
A tubular K member definitely makes life easier but again it's not needed. My first time I did headers was like an 8 hour install with 3 of us. Now we can knock them out much quicker if needed.
That being said I'll be buying a set that I can install on the engine stand and put in when I stab the motor and trans all at the same time. I've done that with a 4v and it was so much easier.