Since the NG units stop at 017, would these not be 018 to 020? The SG units are now 118 - 122.
So far the last two digits of every CBH locomotive match the last two digits of its builder's number.
Any standard gauge unit could be fitted with narrow gauge bogies if required and would presumably be numbered in the 018 to 022 range.
Equally any of the NG locomotives with 78 litre engines could be transferred to standard gauge, so taking a number in the range 112 to 117.
Apart from the bogies (and traction motors) 012 to 017 and 118 to 122 are identical and only software changes are required in the electrical system to cope with the larger motors.
The coupler height would be different but I believe this can be adjusted.
In theory, any of the 60 litre locomotives could also be transferred to SG if required, and if an engine failure occured, a 78 litre engine could be fitted if no 60 litre replacement were available, since all locomotives have the larger radiators required by the bigger engine.
However to meet the weight requirements for the lighter grain lines, the locomotives need to have the smaller engine. It is this type, MP27CN, that Trains Magazine indicate the three additional locomotives to be.