how can I tell what year my frame is?

[strokenit]

How can I tell what year my frame is I bought a 1968 truck when I looked up the vin it says the trucks a 6 and 2wd . so I think its a difrent frame. I want to get a lift for it but the suspension on a 69 is different then a 68 The one thing I now it has front drums not disks I no the disks dint come tell 70-71 any one no how to tell the difference thanks