Heater Core - What next?

I am in the middle of replacing the heater core. I removed the dashboard and now I am looking at the heating and ventilation unit. How do I get to the heater core? I don't see any screws. There are just a few clips. The repair manual does not give much detail either. It says "Locate and remove heating and A/C unit fasteners at bulkhead". How many are there? Where? I just cannot see how is this thing coming apart. Thanks.

What car are you working on ???

It is 1996 B4. Sorry, I forgot to mention that.

Meanwhile I figured out how to do it. I was overlooking a screw that was hidden under the silver lining of the bulkhead. Once I found it I was able to take few clips off and the unit came out. The job is not too difficult but ... I just don't get. Does it always have to be this time consuming to replace a heater core? You are taking parts out for hours just to get to it. Anyway, this is not my favorite project!

Another question... I noticed that the flaps that control the air stream have some foam on them. The foam is almost gone and I was finding pieces of it for past few months in air vents. I took the foam off completelly and now I am concerned that it will rattle. Any suggestions on what to cover it with to avoid the noise? Flaps have holes in them. If I decided to cover the flaps wih new lining does it have to be covered with something that the air can go through?