Both trucks are 370 series which is an 18,000 lb GVW truck. Yours is a standard cab, a 370 (manual trans) or M370 (Hydramatic). The one in the original post is a COE or Cab Over Engine. The COE truck is an F370.
Look carefully at the front axle placement. The COE axle is almost under the windshield:
Check out P. 54 (document P. 52) of this reference:
http://www.1955gmc.com/1955-59gmclit...5NewModels.pdf