Reading that post again, it sounds like I can't tell the difference between their shapes but in my defence, your honour, it was going based on the sounds, and it was a rather tight connection, and I had just been on a rather busy train through the tunnel on the SVR behind a 37 in the buffet car so was still trying to stop my ears ringing*, and, and, and...Don’t you EVER get those mixed up again!
Now you mention that, it's incredibly obvious. How had I never realised this before?!Diesels are really easy; the lower the number, the smaller the loco!
-Peter
*(from both the sound of the engines and the men, many of whom had, shall we say, visited the bar at some point on the journey - how so many managed it in the ten minutes from Kidderminster I'll never know...)