Need pipe advice for a 1930s-ish Round Oak cook stove

[Courtyard Cordyard]

The heavy iron piece coming out the back is rectangular. It has the letters R.O. followed by 4 numbers distorted by corrosion. Attached sliding air control piece has a similar code- R.O. 8932.
I want to attach appropriate found or fabricated that can transition to round conventional pipes.
I don't know what this manufacturer coding means and searches have been futile

 

[begreen]

Check with the antique stove repair places online to see if they have the part. My guess is that something will need to be fabricated. It may need 7 or 8" stovepipe depending on the firebox size and flue outlet size.