Here's a page with a few 6-to-8 swap items:
WH Shameless Plug! that can get you started at least.
The frames were basically the same in this regard, so it does not matter which one gets swapped. If one is in better shape than the other, then that can be your starting point.
As mentioned, if you have correct titles to both, then again, either one can be used.
The bodies will swap directly from one to the other. I don't think the '67 has the decal, but the '69 will have some VIN info on the driver's B-pillar I do believe. Unless it was painted over.
I forget which year got the full info decals, but I know the '68 only had a basic detail, and pretty sure '70 got the full Monte. Maybe '69 did too?
Of course, the decal can be removed/replaced, and the warranty plate on the glove box door should stay with the frame, but that gets you most of what you need.
Paul