Below is my ac unit and the return duct that connects to the blower. I currently slide my 1-inch filter under that pvc pipe that's inside the furnace. PVC is in the way and there is no L-shape latch in the back of the furnace for the filter to hold, its only only in the front. So the filter gets sucked towards the blower. I decided to install 5" media air box outside between the furnace and return duct in the picture where 1 arrow is pointing.
Problem is, the return duct that's marked as 2 in the picture is not coming down straight, it leans towards the right which is why they installed the green flex duct or whatever its called and I won't be able to install the 5" rack like this because there will be some space in between. I have move the return duct to the right by couple of inches, Can I simply remove the duct and align it then cut the top duct by few inches and cover the old space?
I will also move the condensate pump to the left of the furnace first.
Edit: Added more pictures
In pictures you can't really tell clearly but that long duct is not straight. It needs to be moved 1-2 inches to the right to make it straight.