86 Nissan Pickup Heater Core Issue

Help, help, help, help!!!!Need help...... My heater core in my 1986 pickup (early model, same as 85, not hard body) is leaking and needs to be replaced. I have disconnected the hoses and removed the 2 lower nuts that hold the unit in place. It appears that there is something at the top holding the heater unit in place, but I cannot see it. The Hanes manual that I have shows a screw in the top back side, but does not say how to get to it.

Does any one know how to remove the heater/heater core assembly and how to locate the screw?