Right - the decks have been cleared, nerves steadied, sinews girded, resolve hardened - and I've made a start on the changes to the left side of the layout, as outlined above. Before the demolition started a memorial photograph was taken, so we can all remember how nice it was before I messed it all up
It was amazing how resistant to tools various the scenery was - I must have built it to a better standard than I remember. Some brute force was required at times. Basically, the concrete beams holding back the hillside at left front were hauled out, the lower stabilizing beam removed, the trees and fence at the top of the hill wrenched from their moorings, sections of the fencing lower down the hill removed, and the hard shell surface removed up to the far end of the proposed building. The side board was cut down by several inches (much as you suggested, JT) and the florists foam hacked out to fit in the side wall of the base for the new building and levelled for the base of the upper level. Finally, the buffers and light at the end of the tipping dock were carefully removed.
It didn't take too long, and I had cunningly waited until mai laidy waif was away for the day, so that I could use the dining room table as a work surface. After hoovering up the resulting debris another photo was taken to capture the carnage.
Next came the interesting part - building up the new features. The first job was to cut a new side board to size, so that it fitted around the fiddle yard and other obstructions. I had prepared a suitable piece of hardboard I found in the back of the garage, painted appropriately, so this job was quite quick. I had also made the left side of the front wall of the base, with egg-box stonework in place and basecoated, so I only had to cut another piece of foamboard for the side wall and one for the upper floor. A trial fit showed that things were roughly how I wanted and yet another photo taken.
The session was concluded by liberally coating the new side board with PVA and slapping it onto the side of the layout over the old one. A few brass panel pins were bashed in to fix it at the bottom, and the layout left standing on its left side with weights and clamps holding everything together. It will sit on the dining table until Monday evening, as I'm off to Lunnun tomorrow, and the hope is that all will be dry and firmly fixed in the right place when I get back. All I need now is a supply of old egg boxes - there's a lot of stonework to do