The Petit Godin will output 20-26 thousand Btu/hr against 50 thousand Btu/hr for the 503 Hitzer http://www.hitzer.com/model503.html
The Hitzer will hold more coal than the Petit Godin and therefore have a longer burn time for the same heat output.
My vote is leave the room and furnishings alone and spend the money on the insert.
If the Godin is good shape it will fetch a few bucks, $450-900 on craigslist. Someone has a Godin posted for $3000.
The Godin is a great parlor stove, very efficient round design.
The inserts were designed to be placed inside a existing masonry firebox and therefore probably do not radiate much heat on the back and sides.
A free standing stove however will radiate heat from all sides and be relatively inefficient in a fireplace.
Hitzer will ship direct if you do not have a dealer nearby and a 503 goes for, last I checked, $1675 plus shipping. The shipping should be low to mid $200.
Hitzer wait time is about 8 weeks now, it was 4 weeks June 26, so you can have it in before winter.
The Hitzer 503 should hold about 70-80 pounds of coal with the hopper.
Can not help with a dealer as the closest to us is over 2 hours away and we will be doing our own install.
Will post the install photos for a little step by step manual.