Antique shop find/ good ?

[Aodenkou]

Gents, I found this hone but have no idea of origin. I have been a collector for more years that I care to admit, the box appears to have age. I would guess its at least 50 to 75 years, perhaps older. The stone is slightly dished out in the middle. I ran it under water with a bit of dish soap to clean it up a bit. I is about 1.75 inches wide and 8 inches long. Running my fingers over the stone it feels very smooth,

I am going to guess that I need to lap the stone. I think there will be a lot of work for that. I have a DMT that is smaller than the stone I need to lap. It's blue and I was told it was a medium grit. I got it for sharping knives. Could I use that?