The 261 was an option only for 2-ton trucks during it's early years (6xxx and C60 series). Jim Carter states that it was standard after 1958 on 2-ton and larger trucks? I'll check a 1960 Truck Data Book later this evening to see on what sized trucks it was optional. It was still available on 4x4s into 1963.

Jim Carter's 261 Tech Tip

Locations of casting codes

Find and check the codes, or post them here and someone will help.

Tim