I don't have a Luger (or Lahti) board stock, but I do have one each of the pistols...
There was a post by someone about a year ago that said a Luger board stock would fit a Lahti...I take that with a grain of salt (yum...salt!)...Here's a couple pics comparing the two...
Also: The Luger lug measures .295" wide and .140" protruding; the Lahti is .300" wide and .141" protruding...The Luger lug has chamfered edges; the Lahti does not...The Luger has a smaller diameter curve than the Lahti...
And the locking slot is in a different position...
As I say, I don't have a stock...but from the relative positions of the lugs, I would say the stock would attach to one at a different angle than the other...
I'll take it on faith that you can mount a Luger stock to a Lahti until proven otherwise...but I'm from Missouri...