Mike,
It may pay you to remove the laser off the top whilst installing the machine.
If that takes a knock it's virtually impossible to get back aligned again.
Those Ferranti's can be pigs to tune.

Early ones were filed with Fluorocarbon, later ones deionised water, whatever happens make sure the ballast resistor box in the bottom is bled before starting, one air bubble and it frieds the ballast resistors, - don't ask.

.