On a sort-of related note (but not really), am I mistaken in thinking that part of the original Welsh Highland Railway (it may have been the Porthmadoc, Beddgelert and South Snowdon Railway) was intended to be electrified - as far back as around 1900?
That would pre-date this by a couple of decades, although if I recall correctly nothing was actually built and the locos were never delivered.
A fair amount of earthworks (and contractors' track laid) south of Rhyd Ddu. The route was also constructed(including the three tunnels) through the Aberglaslyn Pass.
The route PB&SS, most of which was constructed, immediately north of Beddgelert was on a different alignment. The reverse curves were much sharper and steeper due to the proposed use of electric traction. When the WHR was subsequently built in the 1920s the route in this area was changed to ease the curves also easing the gradient to a mere 1 in 40, I wonder what the PB&SS gradient was going to be! South of Beddgelert the route was changed too, the original bridge over the road still being extant as is a pair of retaining walls standing in the middle of a field with no embankment leading to them!
It is due to the need for clearence for overhead wires that caused the Aberglaslyn tunnels to be built to such a generous loading gauge that now enables the large Garrets to run through them.