John:
537 was the last of the Burlington's narrow gauge locomotives and was leased to the C&S in 1930 when the Q's 3' operations in the Black Hills were abandoned.
The C&S was in desperate need of additional motive power on the mainline operation between Denver and Leadville, and the Burlington refused to allow any expenditures for any sort of new motive power to keep the C&S narrow gauge in business.
537 was badly wrecked in 1927 and rebuilt by the joint CB&Q/C&S shops in Denver. As all engines in service in the Black Hils were required to burn oil, 537 was converted to burn coal in 1930 for use on the mainline. 537 was too heavy for bridges west of Golden on the Clear Creek branch, and there was no way to refuel an oil burner west of Denver on the mainline. To make the conversion, the tender from B-4-D class engine #70 was used, and 537's tender was put on 70, which was converted to burn oil. After the conversion, 70 was used on the Clear Creek branch, and in and around the Denver area as a switch engine and in local freight service.
537 was an older version of the Crystal River engines which later became the D&RGW's C-21 locomotives #360 and 361.
The tonnage rating of the 537 was slightly less than the C&S B-4-F class engines 74-76, which were rated at 145 tons on a 4% grade. Firemen on the C&S "East End" between Denver and Como loved the engine because the big square firebox fired like "Broad Gauge" engines they all worked with in and out of Denver. Firemen on the "West End" between Como and Leadville hated 537 because it fired differently than C&S engines with their long narrow fireboxes. There are no accounts I know of anywhere that 537 was not a good steamer, she was just harder to fire for those who never worked on engines with a square firebox.
For more information, check out the history of No.74 at Bill White's RGS Technical Page website.
www.orci.com/~bdwhite/
I hope this helps answer your questions. 537 was a great little critter. Too bad she didn't survive.
Mike