O had two J50s both Keyser kits with scratch built chassis. They were J50/4 so had white metal hopper bunkers from the manufacturers of the LNER Q1 tank. Millholme I think. They both ran superbly, but in 2014 the motors on both gave up the ghost. I built them in 1974. When the Hornby models came out in 2015 I was delighted. They have been modified to look more realistic including bunker handrails. They run very slowly and sweetly.