I picked up a GE SpacemakerXL ( model# JVM1630WB006) over-the-range
microwave used, but not the installation manual. I have all the hardware
and do understand how to hang it.

The old vent hood that I just removed didn't vent to the outside; it just
filtered the air and recirculated. This is how I want to keep it since I
don't cook that often and when I do, it's usually just to boil water.

The microwave has a rectangular opening with a flimsy metal door over it
which is the output of the vent if going to the outside (up through the top
cabinet). Since I just want to re-circulate, can I just leave it as it is,
or do I need to close that off more securely.

Here are pictures of the top of the microwave:

http://i70.photobucket.com/albums/i9...f/IMG_0011.jpg

http://i70.photobucket.com/albums/i9...f/IMG_0009.jpg

http://i70.photobucket.com/albums/i9...f/IMG_0007.jpg


or should I just remove the metal door frame completely as shown in this pic
and install it that way:

http://i70.photobucket.com/albums/i9...f/IMG_0012.jpg