My 6 inch range oval measures 7 1/2 X 3 3/4, That works well with 6 inch ovalized.
To be sure, measure the oval with a fabric seamstress type measuring tape. 7 inch pipe measures 22 1/2 circumference. The oval should be about that at the bottom when tapered.
First, it's a
coal burning range. You "can" burn wood, but don't expect holding a fire overnight and pieces need to be small.
It also depends on the size of your chimney. If you have 6 inch flue, this adapter should work. (6 inch insulated chimney will work best with coal) You didn't fill in your location, so it is impossible to tell you if any reduction is legal or if a new inatallation of an unlisted appliance is legal in your area.
www.acehardware.com
I'm sure it was originally designed to use 7 inch chimney for that range, by ovalizing a 7 inch piece of pipe. Best to put the damper above warming oven so you reach over the top for it. You would use a pipe surface thermometer burning wood, not needed for coal since it would barely read 150* during normal use. (expect it to read about what the oven temp is with oven on) It is best to use a pipe thermometer of some type if you never cooked or used a manual fired oven, so you know when you have enough draft to circulate around oven and when to shut the oven off if temps drop. Definitely all about the chimney.