The mystery shave is a coachmaker's rabbeting shave.  This one is set up
with skew blades, right and left, making it more efficient for cutting
across the grain -- it's like having a left and right hand dado plane.
Never seen one of these before, but I have a couple of coachmaker's
rabbeting shaves, one with a fence to guide the width of the rabbet, and
a coachmaker's router.

The other, not having two skewed blades, is fundamentally the Stanley 
68.
The odd thing is that other than the Stanley, most of such shaves are 
either
shop made or special order, it seems.  One of my rabbeting shaves has a
Stanley SW blade, in fact.

Those I've seen listed by antique tool dealers tend to run $100 to $300 
a
copy.

Mike in Sacto