the biggest body difference from 67-68 to 69-72 is on the hood and fenders.... the hood for 67-68 slopes down more in the front that the hood on 69-72 models.... this also means that the whole front clip is different as well, including front fenders and radiator....
the 67-68 trucks have a dash that supports a manual choke knob, and thus, the dash has three knobs instead of two (choke, washers, lights)....
the 67 has a lot of 'leftover' traits from the previous body styles such as smaller rear windows, a different looking cigarette lighter, different looking armrests, different rear-view mirrors, and even different dash knobs....
the hubcaps in 67-68 were also different than those in 69-72...
the seats were generally different esp. in their stitchin style from 67-68 to 69-72...
i think a lot of the engine options over the years have changed as well, but i would have to go check the red book (which i dont have handy here at work)...
i hope this helps ya out!
(BTW, i own a 68, which i feel is a unique creature among all the years of the trucks, just like 67's)
jewels.