9a end gear mesh

Hello all!
I have a 9c that I am converting to a 9a.
Problem is I pulled the lathes apart 2 years ago and after moving house I have decided to put it back together. All the parts were cleaned, oiled and packed up for the move and no parts are missing.
Yesterday I rebuilt the qc gear box and bolted it to the bed. I installed the reverse tumbler with 20t stud gear, the banjo bracket with 80t idler and the 56t / 40t gears on the end of the qc gearbox.
Problem is when I bring the idler in to mesh the gear doesn't line up with the tumbler stud gear and will interfere with the inner gear. It also doesn't line up with the 56t qc gear.
Can anyone tell me what I'm missing?
For now, I have taken the washer from the 80t idler and placed it between the banjo bracket and spacer to bring the gear away from the inner tumbler gear but the alignment between the 56t, 80t and 20t gears are staggered and I don't know what I'm missing.
Any thoughts on how to correct this?
Thanks!
P.S. I have a picture but don't know how to post it here

Can you simply loosen the headstock and slide it to where the gears line up?

Chad's got it- slide the headstock.

allan

Great! Never would have thought of that.
I guess the plane of the gears must be different from a C to A model?
Well I'll tackle that job tomorrow.
Thanks guys!

No, the plane is not different, there is just no feature which locates the headstock along the length of the ways.