I am not sure if you will be able to use the ventmaster in this situation. The collector is huge and there is a metal strap on the bottom of the muffle box that would cause all sorts of problems with the lower compartment of the kiln.
In my situation, I did the opposite by drilling two 1/2" holes in the bottom of my SC3 for airflow and I have an in-line exhaust fan connected to some metalized film flexible duct tubing above the vent hole in my kiln.
On Paragon’s website and YouTube you can find some information that shows you how to replace the muffle. There are a lot of screws you need to remove and sheet metal that needs to be shifted around to get to the bottom of the muffle box. Electronics and wires need to be moved to get a clean opening for your drill. You will need some good sharp drill bits with a little oil as a lubricant to get through the metal outer cover of the muffle and cutting through the fiber is easy, but it creates a lot of irritating dust, so use a dust mask to avoid breathing in the fibers.
It has helped with combustion air, but I probably would drill two more holes in the other corners to allow for more airflow during burnout. Not sure I want to take it apart again…
I hope that helps!