Just to add to this in a "don't do what I did" kind of way:
I am building my own scuttle, this presents a couple of problems with the book design - the first is that the steering column comes to close to TR9 to allow the scuttle cross member to fit without cutting it to allow the column to pass through. The second is that the steering column support bracket can not sit on top of the top rail as it would get in the way of the scuttle. It is far better to make the steering support so it welds on to the side of the top rail (like shown in Dogwood's Post) if you are fitting a fabricated scuttle.
I will have to cut mine off and do it again - a complete bitch as the chasis is painted.
Wish I had thought of it earlier.