That's the left side duct work that you need. Always in the name of Race Car things get remove & tossed with seeing the car was no race car. Hope you got most of the heat-A/C set up.
I believe the guy took out the A/C to get the LS swap done. However by the heater box area, I feel there is more than enough room to have kept the A/C. Eventually I will have to remove the gauge cluster to get this duct in and any other missing ones in to get the A/C reconnected. The instrument panel is off right now for me to try and get the gauges working with the LS swap and upgrade the bulbs to LEDs, and I am eager to get it back together.
Need to try and get these 3.5" speakers in now, looks like I may have to go with speakers with smaller magnets or try and load the speakers in from under the dash.