"Unless it's an early one that has two separate jets rather than the twin jet in the middle."
One of the easiest, cheapest and most effective modifications to make to a 90/110 or Defender is to replace the two single-jet nozzles or single twin-jet nozzle with a pair of twin-jet items. The holes are already in the bulkhead and the standard pump is more than powerful enough to deliver the water at the necessary pressure.
I did this soon after buying my 90 11-years ago and haven't looked back since and everyone I know who has also done it comments of what an improvement it is. It is especially useful if your screen is covered in a lot of muck as the additional water really softens it allowing the wipers to do their stuff.
By the way, I agree that removing the top of the dash is by far the easiest way to replace the nozzle, it is done in a matter of minutes and saves all that fiddling about.