Thanks, Ron.
Mg_Bizzle: The speedo cable is in JUST the right place to block view of the heater box left (short) edge, but it looks as if that side tab is missing on the box... There are three screws across the front of the box and one in each side. Have you undone the one on the blower side, UNDER the cage area? It's a bear to access (or even SEE), and that may be what's holding you up?
...just trying to suss why it won't release...