Here is a picture of the front and back of a CLAYTON cast iron door.
If you try to modifiy the door I feel it may be pretty difficult to do without cracking it. The brand new replacement feed doors from the U.S.STOVE aug. 2006 price sheet go for $175.87 and that is without the handle. If you want a door with a viewing glass, you are going to have to have it fabracated out of steel. They can do wonders with these new cutters. But expect to pay well for it. Don't forget the smoke curtain hanging on the inside. It takes up half of the door. There is no air wash inside the stove to help keep your glass clean. So, I wouln't expect your glass to stay clean very long. Especially, if you don't run hot enough or are using moist wood. Just something to think about.