Cabin Air Filter - Where is it.

I have a 2000 C3500 Silverado.
I remove the screws under the passager air assembly and when I opened it I found the heater core but no filter.

Do I need to dig more into the box ?
Can I get to the air filter by removing the glove box?

Does anybody have a picture of what / where the air filters goes.

I have found web sites on the internet that show for a 1500 but I guess the 3500 is different for a 2000.

Thanks in advance for any help you may provided.

Called dealer and there is not one for the 3500 for 2000