"the longer flight near WH Smiths is a little harder to resolve, would be one hell of a steep ramp."

The original subway had no steps so it is more than possible.
There is quite a distance from the rail and road to make a reasonable slope.

The German/Iron bridge is disaster waiting to happen - the steps are very steep and to make matters worse, who ever repaired the bridge a few years ago neglected to put the hand rails back. All 4 are missing from the top of both sides. It probably could do with a cage over it as well, to deter objects being lobed over - there was an old bike by the line a few months ago!