Bruce, I just thought of another scope mounting option. The DNZ #12042 one piece mount made for the Marlin 1894, 1895 and 336 has a flat base that would fit quite well on an octagon barrel. Though it's a bit expensive, it's a great mount and the cost is somewhat mitigated because you don't need to buy rings for it. It would require drilling and tapping at least two holes to mount on the barrel.
See it here:
http://www.opticsplanet.com/dnz-dedn...ope-mount.html
Here's what it looks like on my Marlin with a 4X scope mounted.
