The pit was cut with a modified jigsaw blade to allow a specific depth.
Of course the track had to be unscrewed and removed.

Then all the wiring had to be removed.

And then the locoshed had to be removed. Had to find the hidden screws.

Vacumed whilst the jigsaw was making dust.

The pit fitted beautifully and a frame of tape around said pit to round off the edges nicely and then painted.
The pit was made from 1mm styrene.