To do this I looked at the underside and measured out how far I could go with a panel. Over the years of Land Rover ownership I have discovered that the bigger the access the easier it is to do the work. You have to watch out for the mudshield bracket on the underside of the wingtop. I settled for 1 foot(12inches) on this job.
The foot mark was transferred to the top surface and tape layed out on the line and next to it to keep the paint from getting marked up. Then a jigsaw was used to cut the wingtop.
So with the panel clamped and bolted in place the pop rivet holes were enlarged to 3/16 and the rivets put in.
The wing to bulkhead bolts were installed so the wing could be fitted. Then I removed the top and bottom ones as they are not a slide fit into the wing. The new access panel was left on and a bolt put in upside down in the top mounting bracket to locate the wingtop, allowing the wing to hang in position.
So the next process was hang the wing, mark the area needing to be cut around the steering box, remove the wing, cut the wing, refit the wing, see where there was interference and mark the wing, remove the wing, cut the wing, refit the wing, see if there was any interference and mark the wing, remove the wing, cut the wing, refit the wing, see if there was any interference, mark the wing........well you get the idea. Lots of fettling around the steering box and the lower steering column.
Even with all the fettling I screwed up and made one section too large an opening. Solving this was as simple as pop riveting the cut off section to fit the needed opening.
It is not permantly mounted because I still need access to the electrics on that side but it does fit.