I think you can still download the 67 chassis service manual from here, not sure if 69 would be much different:http://www.camaros.org/forum/index.php?topic=9433.0
My car has an access cut-out, from a PO or repair shop prior to 1986. Must have been the thing to do back in the day. I pulled my AC suitcase a few weeks ago to restore, it was a major PITA. I still had to nearly remove the fender to get to all the box fasteners. Don't have the kids around when you do this
. If you pull the "suitcase", you'll need the strip caulking or whatever it's called to reseal the box. You can usually get this from a local jobber. As JK mentioned, you will likely need to replace other old seals as well. Take your time, you won't want to go back in a second time.