Here's s photo of the first 4 parts fitted to the axle. This all relatively straight forward. The red marks show the lowered cutout on the Shift Cage (#2) to allow the outward facing hook to be caught by the upstand to the right of these marks. The part marked in green is the inner spring cage (#4) - which will rotate CW against the override spring if the shift is impeded, if which case the green upstand will engage with the shift spring.

Fitting the shift spring is the next part of the puzzle. There are two isues to be resoled.

First, one hook is longer than the other - does the longer hook fit facing the axle centre in which case is it long enough to contact both the shift cage and the inner spring cage ? Or does the shorter hook fit here to provide rotational clearance.
Some experimentation is in order.

Second, how far does this spring need to be rotated to provide sufficient tension to the shifting cable. And how to do this while attempting to fit the upper spring cage to capture the tensioned spring. Note that the upper spring cage cannot rotate as it is keyed to the axle so I can't hook the spring to the cage and wind it up.
This is the part I'm struggling with, so I'm really looking for some guidance from folk who have attempted this before. Otherwise I think I'll need to make some type of fitting jig to wind the spring up, clamp it in the tensioned state, and then fit it without letting go of the tension !