plumbing for ceiling showerhead
Everything is simple in theory. Without being there we can only speculate.
What may be easier in your case is to :
1: Mount a wood block where you want the showerhead to come out of the ceiling. Make sure it is level and all that or the showerhead will look like an inebriated plumber installed it on the weekend
2 : Cut off the showerhead fitting you have leaving enough pipe to attach to.
3 : Run a piece of soft copper from cut end to cut end, and solder on couplings and/or 90 as needed .
If you have lots of room overhead, you may be able to eliminate the soft copper, but it does eliminate a solder joint.
If you mount the block, and hire someone to do it, I bet this would be just a trip charge + materials. Moving showerheads is pretty simple business.