That is correct; it is too big. The i7-960 is designed for a motherboard that has a 1333 pin processor socket whereas the DH55TC motherboard has a 1156 pin socket. One of the major differences that accounts for the pin difference between the two is support for three memory channels in the 1333 pin processors whereas the 1156 (and 1155) pin processors support only two memory channels...
Following up on my previous response, the i7-960 processor can be used in any of the boards that have 1333 pin processor sockets. This includes DX58SO, DX58SO2 and DX58OG. As for the DH55TC motherboard, the list of compatible processors can be found here: http://processormatch.intel.com/CompDB/SearchResult.aspx?BoardName=DH55TC.