NH 66 Knives Question

Hi- first time posting on here but have been reading and learning from everyone here for a few years. I do a few acres of grass hay every year for a few mini Herefords I raise. I bought a NH 66 baler a couple years ago and have been learning as I go with this and trying to make better hay.
I’ve been reading about sharpening the baler knives and figured I should take a good look at mine. The stationary knife looks like the pictures and videos I’ve seen related to knife sharpening. It has a good clean edge and seems to be reasonably sharp. My question is about the plunger knife.  It is squared off with no angled knife edge, and saying it is “squared off” isn’t exactly accurate because the edges are rounded smooth.  Before I order new knives for this I wanted to ask about sharpening the current knives. The stationary knife seems obvious to follow the current angle and just clean up the edge. Should the plunger knife just be ground with a flap disc back to a square edge with crisp corners?  Or should it have an angled knife edge opposite of the stationary knife?  Or something else?  I can’t find a good picture on the NH parts lookup website to compare to mine.   And I’d want to check knife clearance of course after sharpening. 
 

I’ve attached a few pictures of what the plunger knife edge looks like at the red arrows. 

NH 66 Knives Question