My wife's 1986 745T (150,000 miles) is about to get an evaporator replacement if I can get the lower cover of the evaporator plastic housing off.

I have a printout of the Brickboard's 2006 instructions which in one place says " ... unless you remove the bolts that hold the HVAC box in place. The evap drain extension is in the way." Then, "when you have removed the screws and you are trying to figure out 'what else is holding the cover,' it's wedged between that extension and the protruding evap drain." by Adam Burke.

"HVAC box" has me puzzled, is that the whole plenum for the A/C?

Also 'drain extension' = 'condensation drain'?

I've removed at least 10ea 7mm screws holding bottom to top, and the 2ea 10mm nuts in the fresh air intake, with no noticeable help. Solid as a rock.

How is it possible to lower the firewall end of the cover?

Gently (relatively) using a pry bar between the firewall and the plenum, it is barely possible to get the drain tube through the firewall.

There is a drawing and a picture showing screws holding the bottom. No clues for removing the 'HVAC' box, other than the 2 10mm nuts.

How then, front end first?

The preceding instructions (2 owners) seemingly had little trouble removing this cover, but difficulty installing the evaporator. (I'm not sure of living through that).

We started out with 2 used 164s, restored them, got two used 745Ts.
So, my wife's car awaits some help, in my garage. HELP!