Help with installing wood burner

Hi All

I had my gas fire removed and I've taken out the surround and hearth to reveal what looks like a fire block sort of thing and block walls to the chimney.

This tapers up and the diverts off to the left when looking up the chimney. Does anyone have any idea what this supports, and if i could make the opening any bigger?

The opening is not really big enough to slide a wood burner back into it, and the block chimney is tied into the inner leaf of the house, so don;t know if I could make it any bigger... any info is much appreciated.

Photos below and attached

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http://tinypic.com/r/cp8cx/8

...Thanks for reading.

I'm no expert on this, but it seems that as long as your exit from the woodstove had a clean shot out and up, you could find an adaptor and use a smaller diameter stovepipe to go up the rest of the way after the chimney tapers off. Here's the first article I found:

http://www.hearth.com/econtent/index.php/articles/installing_a_woodstove