the good news is the blower box will come out without removing the dash completely. 3 nuts and a few wires, one cable. loosen the dash on the passenger side and you should be able to wiggle it out. I just took mine out like that.
the bad news, I was just looking at mine trying to replace that flapper seal. I don't think the flapper will come out of the box. It looks like the plastic was molded around the door pivot.
I've got my entire interior (dash included ) removed right now, cleaning up from a mouse infestation.