Sam,
The AC-9 and the Challenger are the two engines in the pictures and are both my engines. The Big Boy is on the outer loop and isn't in the picture. I have collected those three engines in the last two or three years and are all among my favorites. The AC-9 was upgraded with a cruise board by Boxcar Bill (here on the forum) and is my favorite engine to run. It crawls like a champ! He did a great job! Thinking about doing the same with the Big Boy! It is a little sensitive and inconsistent, but still a great engine.