Saab: Remove and replace heater core, saab 900 turbo spg, negative battery cable

Question
This is a 1985 Saab 900 Turbo SPG.  I am stumpted, I am not able to remove the diffuser duct that runs from under one side of the under dash to the other. I have removed all the screws that I can get to, it seems there is one screw holding the diffuser up under the dash that is unreachable. The screw appears to be just above where the vent door exposes the heater core. It appears that I have to remove the lower dash (the one covered with a leather material)it looks impossoble.  I need direction, I called the Saab dealer in Kansas City but they were no help. If you have any ideas on how to expose the heater core I world greatly appreciate it.
Thanks, John

Answer
Never done it myself, but try this link http://www.thesaabsite.com/c900heatercontrolvalveproceedurebottom.htm

I also pulled the following instructions for a 92 Saab. Hope this all helps.

Heater Core
REMOVAL AND INSTALLATION
900 Series
1. Disconnect the negative battery cable
2. Remove the dash panel under the switches on the steering column and the lower section of the instrument panel.
3. Remove the air diffuser and retaining screws.
4. Remove the left defroster and speaker grille.
Remove the control rod from between the coolant shut off valve and the control rod by sliding the rod
as far forward as it will go to free it from the knob, then pull it rearward to free it from the shut off
valve.
NOTE: The plastic joint at the control knob is accessible from underneath once the switches below the
heater controls have been moved backward.
5.
6. Remove the lower section of the heater housing.
Drain the coolant and disconnect the hoses. Plug the ends of the hoses to prevent coolant from leaking
into the compartment.
7. Separate the heater core from the housing and guide it backward and downward. It will be necessary to
disconnect the brake pedal return spring and depress the brake pedal slightly.
8. The water valve and the heater core can be separated after their removal. Do not kink or break the
capillary tube.
To install:
9.
10. Carefully guide the heater core and valve assembly into the housing.
11. Connect the heater hoses.
12. Install the lower heater housing section.
13. Install the control rod to the shut off valve.
14. Install the left defroster and speaker grille.
15. Install the air diffuser and retaining screws.
16. Install the lower instrument panel section.
17. Connect the negative battery cable.
18. Start the engine and check for leaks.
19. Recheck the cooling system and adjust, as required.