I bought a 1903 M/S 6.5X54 with a similar dovetail cut in the receiver ring. However, someone had replaced the claw mount base with a dovetailed blank which was rounded to match the receiver ring contour. I have had no problems with it.

Whether you can live with the replacement stock is a question that only you can answer. For a purely utilitarian hunting rifle with a good bore $800 doesn't sound like a bad price, but I wouldn't hesitate to try to negotiate the price down, given the "problems" you describe.