I have the Swedish Husqvarna M40 and it does have the accelerator.

It also has the round barrel shoulder.
I do like the looks of an 'artillery' Lahti...
Here's a couple pics of the barrel stub compared to the Luger. The Luger barrel stub is ~.748", while the Lahti is ~.906". Three cuts in breechface on the Lahti; extractor, ejector, and accelerator.
I think a Luger artillery barrel has enough 'meat' to cut away to fit the Lahti barrel extension. I don't have one loose to mic, but I think there's enough.
Awkwardly placed slide safety; it cuts into your thumb when you fire it.
Wups! My mistake; the cut on the barrel face at 12 o'clock has no function in my model - it's not for the ejector. The cut at 3 o'clock is for the extractor, the accelerator cut is at 9 o'clock.