Scott's pictures are almost identical to my situation. Thanks for them Scott !!! Only difference in mine is that the top course of bricks has the small end of the brick facing out. I have about the same amount of gap on the sides as on the right side of your stove. We have an 18" ledge about 12" off the floor upon which the stove is currently sitting on. Puts the front edge of the stove right to the edge of the ledge.
Scott I forgot about the baro as I wrote this. It would have hit me later on. But thanks for the reminder.
Due to a chimney fire several years ago, we are opting to install a S.S. flexible liner from the top which will connect directly to the stove. Then all I have to do is seal off the gap at the existing damper. I 'm pretty sure the liner will be cemented in place at the top.
This has to be idiot proof. She has never operated anything other than a thermostat for the oil burner. And I'm sure I'd catch hell from the wife if I was over there every night.