I was about to ask about the strange tender side, but decided to look for an answer first. Here it is, in case someone else is wondering, too.
From:
[
en.wikipedia.org]
The Class NG15 had larger tenders than the Class NG5 with a working order weight of 31 long tons 4 hundredweight (31,700 kilograms), compared to the 25 long tons 11 hundredweight 3 quarters (26,000 kilograms) of the Class NG5's tender. The tenders had low-slung sides, with the bottom part of the water tank extending down to below axle level on either side of the tender bogies to lower the vehicle's roll centre on the narrow track gauge.
Bruce