They are a real biach to get back in!
If your pics are where you are presently at, you'll need to undo the 2 pipes to the evaporator too. And pull the dashboard.
The studs you're looking for can be seen from the photos below.
This is a view of the firewall side of the RHD HVAC unit. Note the 2 studs next to the heater core inlet, and the stud directly below the evaporator (little yellow circles).
From a slightly different angle, note the little yellow arrows.
This model had 3 studs; some 740 HVAC units had an extra stud (IIRC) midway between the evaporator and heater core.