Heater Core-ectomy Gory Details Part 2

[mwoodland at Valicor.com]

With the heater box now exposed, make a cut (#1) directly behind the metal
hold-down strap, as close as possible to the raised trough that contains the
strap. If there are triangular reinforcing gussets, cut through these also.
The cut will extend across the top. and down the drivers side to the top
left corner of the opening for the heater core inlet/outlet. 

This same cut (#1) will extend down the passenger side, to a squared off
protrusion on the heater box. (Here's where the photos would help..)
With the air flap cable disconnected, actuate the linkages by hand to move
them out of harms way. Cutting these off would be a bad thing.
A series of cuts can be made from the passenger side, the first from the top
left of the protrusion, in line with the car, straight down, approximately
1/8" in from the edge, to ensure that you are clear of the left wall. Extend
this cut forward, across the top, and down the front of the protrusion.
Continue the original cut (#1) down the passenger side, and tie this cut
into the cuts around the squared off protrusion. At some point, it may
(will) require tool abuse, i.e. the use of a screwdriver, thin chisel, or
stiff putty knife, sharpened, (or not) to an edge, and used to punch through
and connect the cuts in this area. The good news here is that the plastic is
fairly pliable, and will not shatter.

The next major incision (Cut #2) starts at the passenger side top rear
corner of the heater box, and across the top of the box to the driver's
side. Due to space constraints (barely enough room for hand and saw, even
with the wiper assembly removed) I cut to a line straight across the top,
intersecting the front of the triangular reinforcing gussets. Extend this
cut down the driver's side, keeping as far to the rear as possible, and
angling forward to end at the top right (rear) of the opening for the heater
core inlet/outlet. This same cut will extend down the passenger side, just
forward of the air control cable support, holding the cable up and out of
the way during this cut. Extend the cut down the passenger side, as far as
possible.

At this point, the whole top piece, with air flaps and control linkage still
attached, will lift up, hinging on the material remaining on the lower
passenger side, and pull up far enough to lift out the heater core. Mop up
the antifreeze and plastic sawdust with a rag, slide in the new core, and
re-connect the hoses.  Once the system has been fired up and leak-tested,
the cut lines can be sealed with Silicon RTV, Goop, duct tape, or <insert
favorite>. Reattach air mixing flap controls, and re-secure the cable to the
heater box.
Heat,.. and not a moment too soon.