Andy was able to give me a measurement and was within 6 inches on my 69 tradewind (ehh I'll give it to him). On mine it was 101 inches back from the first rib, about a foot behind the rear vent, but not sure on a 68 since I think there was a body style change. I cut the hole myself, reinforced it, installed the AC all in a couple hours. If you have access to a couple sturdy ladders and some basic tools like tin snips and something to cut some aluminum stock to add bracing (sawzall or hack saw) then you should be able to do it. I'm a total rookie and when I got into it I realized how easy it was. I posted pics of it on the thread
http://www.airforums.com/forums/f427...day-35176.html