I got the dash off, the steering column down but I cant seem to get the heater box open to get to the heater core and the A/C. anyone know what im missing here ive been staring at it for about 30 mins now.. Its an 87 5.0

 

man i did my 83 gt like 8 times but in the day ill have to look at my old case but i think some haver a door. or maybe someone cut this on 91 i did you didnt even have to split the case . dealers to it .

 

in the 87-93 you gotta take the dash off "the new nos/man"

but i just did mine the other day. its kind of a bitch.. after you pull the dash back you have to pull back the "ears" to the ac unit on ur firewall and un do thoes nuts (both sides) its to the lower left from where ur core tubes come out.. then you have to undo the 2 screws on the black box where ur core is and pry it open (its rather stiff) and use a deep socket on the right side to help keep it open. then pull up on the lfet side and pull it out..

this site tells you exactly how to do it w/ pics
http://www.mustangmonthly.com/howto/5652/photo_01.html