Good score! They're nice little rifles, always were underappreciated. I have a 673 in .350 mag, have no intention of ever parting with it. The 673 is a 3-part designation: "6" for it's M600 lineage, "7" for it's model 7 action, and "3" for it's year of introduction (2003).
The 673 is a bit heavier and sports a longer 22" barrel, but is still a pretty handy rifle. I don't honestly think I'd want it much lighter than the 7 lbs it is in .350 mag.
I'll bet a tinkerer could fit a 673's steel rail to it.