Fitting of the steam head

Can somebody advise when and how to fit the steam head. I've assembled the horn plates and front and rear spectacle plates and shaft tube etc. as a sub assembly and painted, but now seems I need to remove the rear spectacle plate again to get the steam head in.
Rss

The steam head is attached with 4 brass nuts and bolts, i put the nuts on the boiler side.
The bottom 2 holes are covered by the boiler so getting the nuts in will become very difficult later.
Just to add to the difficulty the steam head has 2 globe valves that will need to be disassembled if not screwed into the steam head before mounting it to the spectacle plate.
In short leave the rear spectacle plate until you have the steam head and globe valves.



Hope that helps.
Simon C