Quick question. Is the subframe for the 67, 68 and 69 all the same (the actual subframe only)?

Minor differences - but, they will interchange.
68~69's have different 'bump-stop' mounts than 67 - easy fix.
Sway bar mounts are slightly different on later supframes.

Check out David Pozzi's website. Here (http://www.pozziracing.com/first_gen_camaros.htm) he shows that even 67 frames are not all equal....

...he shows that even 67 frames are not all equal....

David has photos showing one of the several "minor" differences in Camaro subframes. Specifically, his photo refers to the lack of a 'tow hook' hole in the inner forward frame rail on some early subframes.
This is not consistant at both plants and doesn't effect the 'intechangablity' of the subframes - which is what I understand to be the question here...
GM changed the part number quite a few times during production. Here's a list of some of the part numbers for the subframe -#3899000, 3899005, 3917526, 39283361, 3930099, 3935096, 3939739, 3954642 & 3965600 - any of these numbers will be a bolt on replacement for a 1st Gen. You may have to drill a couple holes though, depending on the year and options...
There are several 'hole' differences between subframes from the different plants over the years that do not effect there use as a replacement subframe on another 1st Gen. Camaro - period.

Hope this helps;
John