More like falling into a black hole in my opinion. Or maybe through the looking glass? ....... Glad to know we agree.
I'd forgotten about GWR stone. Probably suppressed the memory, as I got exposed to it at a sensitive age, when I discovered there were such things as model railway magazines and then found that in the letters page.
To get back to the point, given what old car engines of my acquaintance look like, pretty much any mid grey with a large helping of oil, grease, coolant leaks, rust and general grot would look about right to go with a rusty grey exterior.
I forgot to ask earlier how the mech design has worked out. It sounded like you were happy with it in an earlier post.
Graeme