I've been thinking about this combination for a few years, and got a little bored with wood working on the Erma boxes over the holidays-so.... I decided to add a take off 7,65mm Luger barrel to a spare T 14 receiver with poor bore.
The combination "works", I had it out for test firing this past week.
The original barrel was cut from the T 14 at the receiver chamber-barrel transition point. The receiver then bored and threaded to 18mm x 20 TPI of the luger barrel.
The barrel flange was "adjusted" to headspace the barrel to the T 14 bolt; the extractor cut then made and the barrel secured by crush fit with a little loctite added.
The original T 14 extractor and ejector work fine; the magazine lips needed to be tweaked in a little to hold the slightly smaller luger cartridge within the magazine.
I wondered initially about the "recoil" of the luger round, since it is a little hotter by fps; and the 8mm Nambu is often spoken of as "weak".
First ammo I tried was Fiocchi .30 luger, it would not lock the bolt open on the T 14/.30- same problem as I have had with some .30 lugers and this ammo.
Next tried Privi Partizan .30 luger, and it worked fine, cycled and held the bolt open as it should; which is similar to my experience with it in a .30 luger.
So it seems with this particular T 14 and its springs, the recoil of the 7,65mm luger cartridge is quite similar to the original 8mm Nambu.