Hi diggerdigzit,

and welcome to TR.
I did all my cursing when I put the clutch back on,
only I was calling myself

Is your problem only going up the box?
Take a look at the quadrant Pawls and springs for wear,
and make doubly sure the quadrant is exactly in the right place on the camplate.
when you assemble the box, put the camplate in the first gear position,
then when you put the middle case on let the quadrant drop down
then slide the case on,
the quadrant may need a little wiggle to get the first tooth engaged, and push/tap fully home.
With a bit of luck, job nearly! done.
