[Shyguy]

The only thing that I know of is that the '67 frame does not have the dimple where the steering box is mounted.

The 1/2 ton and 3/4 ton frames are slightly different in the height of the rear cab mount on the frame and the 3/4 frame has extra bracing on the cross member where the trailing arms mount and usually the trailing arms are a little beefier.

Danny

Edit:

No GMC frames are not the same in most cases because most GMCs had leaf springs instead of coil springs like the Chevys, but they can be made to work.

Here are the pictures the first one is of the 67 frame with no dimple for the steering gear.

The second one is of the 68-72 frames with the dimple.

The third one is of the 1/2 ton rear cab mount.

The fourth one is of the 3/4 ton rear cab mount.

The fifth is of the 3/4 ton cross member with extra bracing.

Hope this helps.