Heater Box Removal
 

I'm in the middle of a blower fan replacement on a 72 280SE 4.5 and have gotten some cryptic hints as to how to remove the box to get at the fan, but would really prefer some solid info. Scoring the box was one suggestion but as to where these incisions are to be made and with what sort of device I've been left on my own. I've removed every bolt that I can see and it moves around somewhat but seems secured in the upper left area, both heater core tubes are disconnected. I'm getting a bit frustrated my Chiltons doesn't cover my model in the heater box section and few people have done this sort of thing.

The heater box is now loose yet still confined beneath the dash and its dimensions seem to exceed the dimensions of the exit areas. Does the dash of the 72 280SE 4.5 come off? I have removed everything but the A/C unit, please not the A/C unit too.