Answer to your two arrows on the picture above (black car) where the heater tubes are visible in the middle of the trunk.
It would appear that the black car is an earlier car than yours.....it has the look of such by the fact that there are two pieces of metal blocking the air flow from going down this "tunnel" and into the car via the shifter gate hole!!!!
Your car has a different design at the point where the heater tubes exit this tunnel and turn downwards. You don't need a cover here at this area as the newer design eliminates the need for it.
You will still need a small cover for the top section. Without, as I mention, air will enter this point, and when you are driving with the windows down, air will blow up this tunnel, now heated by the heater tubes, and will warm your cabin....plus blow up the shifter if the boot has any cracks or gaps. Look for evidence of prior holes to mount a simple cover with.....
Also, over by the pedal box, look for ways to cover points that would allow air to come up and into the cover for the pedal box area. Around the speedo cable....brake lines..... You will want to seal these areas off with some of that metal tape with the thick goop on it used on air conditioning pipes.... or similar.
If you don't, hot air from the radiator can blow up these areas, into the foot box and back down on your feet! Turns a Goose into an oven very quickly!!!! "Roast driver's feet"........not good! You may also find an air leak in the center of the steering shaft! Mine was hollow! I stuffed a small piece of foam in mine to stop from roasting my knee! There was air coming out of my upper u-joint area!!!
I've posted pic's of my "closed cell foam" creations..... various thicknesses used, slots where things need to pass.... generally made the pieces a bit over sized so that friction holds them in place.
Doing this cut down on heat coming into the cabin by about 90% or so. You can't quite seal it off 100% because you need openings in the foam for your activator rods and such....BUT, you can cut down the airflow by doing this, or similar.
One note on the big yellow parking brake pulley at the front of the black car...... I had this on my car and always thought it was something added later..... I think the parts book says it was sourced from a Fiat 500 or so....... and I figured that mine broke....and someone carved this up out of fiber board or such plastic..... Nope! That's Italian original!