All o' them B-4Gs.

Through my spurts of periodical internet steam research, I've started to gain an interest in the B-4G class. They're like scaled-down K-36s, as someone else pointed out. According to Steamlocomotive.com (which any railfan should bookmark, btw), there are no less than four in the states of Colorado and Alaska. But, other than what units are surviving, I've found little information on the engines themselves. What is the history of the B-4G? Also, what does the future hold for #44, #111 and #69? (#40 excluded, seeing as she's operating under the quite capable eyes of the CRRM).