Hi again Jeff,
Thanks for getting the down the valley shot - not sure why, but I'd put my last post in when only Jason's first post was on this page, yet mine now appears halfway down, maybe it's a factor of doing it on my phone.
Anyway, I think the photo shows the concerns Jason (and I) had - if you compare the two sides, the hill is a lot closer to the viaduct on the right. Yes, in the photo of Arten Gill the spoil does come close, but not quite as close as you had got it. Glad to hear you are planning to cut it back a little. And I agree with the not annoying the neighbours with late night power tools - it stops you being able to complain at their late night carousing!
The spoil heaps to the side of Arten Gill are interesting - they appear to be completely flat on top, steep sided, and at two levels, the lower one is at track height, the other near the height of the top of the cutting, and they are quite big (bing maps' aerial view suggests over 200 feet long) - I'm looking forward to seeing your representation of them!
I'm not convinced you have to loose the ability to remove the corner - it just needs a bit of careful thought and planning. Andy's bowler hat idea has some merit - if the lift out part runs up the wall somehow (drawer runners?), and a way of minimising the resulting joints can be found, you could keep it as an emergency access... How much would it need to lift by to give you the access you need?