I don't know about a 67-68, but we are in the process of doing this on my son's 69 right now, and we have everything out, console, dash pad, lower dash, and everything back to the heater. This is a MAJOR project. Be sure to plan it well to avoid big problems. Lucky for us the heater was not connected. Otherwise, we would also have taken out the front seats and carpet because of the antifreeze mess. This can be very messy! Good luck.
Well, I tackled the removal just now and to answer my own question... the heater box can be removed without removing the console! A lot easier than I expected as well ... and I found my leak !! Too bad I have to get a new heater core, but at least it shouldn`t leak anymore