Lionel's 2-6-6-2 is a USRA mallet. The C&O had 20 of these originally numbered 875 to 894 and gave them their H5 class number. In 1924 they were renumbered to 1520 to 1539. There is a picture of 875 on page 144 of C&O Power. Lionel's model of 875 is pretty close to the prototype.
Ken