(16 Jan 2020, 11:38 am)JP6004 wrote No reason for X1 to be low height, X30 has to be for the low bridge at Dunston
Exactly, but as others have said they may go down the route of all low height.
Even still, 6337 can still fit under the bridge in Dunston, although only just, you can hear how close the roof is when you go under.