The Oxford Rail J27 is an excellent model and something of a bargain to boot.
I picked up an Early Crest example when they first appeared. It ran smoothly and had no problems when running in.
Looking through The Last Years of North Eastern Steam by Tuffrey I found a suitable prototype to model in the form of 65802 of Percy Main shed photographed at Blaydon in fairly clean condition.
I wonder whether Oxford Rail will offer versions with modified boiler domes