Any info on this?

Milpar Col U.S. M6

There is no latching mechanism. The numbered grips don't have slots in them.

 I found one reference that said Milpar made a small batch of these to be used as fighting knives. 

 Legit?

I wish I knew.  These grips usually appear on M5/A1 bayonets, turning them into a "fighting knife".  Most of the opinions I've heard are that these were offered to the public as "camp knives".  Not unlike what was done after WWII with the left over M4 and M3 parts. According to Gary Cunningham's information, the numbered grips were introduced in 1964.  They are interchangeable between the M5/A1 bayonets and the M6 bayonets, however, he said, most M6 bayonets have unnumbered grips.

 

It appears that this modification was done by the factory, or by some other entity, since not only are the grips modified, there are metal spacers on each end of the tang to presumably, take up the space between the cross guard and the pommel where there is usually a gap on each end of the grips. 

 

I can't imagine that this is a military item, since the whole point of a knife/bayonet was that it would already have a dual purpose.

Marv