WOW That is one sweet M23 !!!
It's more the engine capacity.
I am actually not sure if the frame is the same. I know I have an article that compares the two models but I will need to dig for it.
The Mk 2 has a slightly larger wheelbase of 1315 mm vs 1305 on the M8
" " heavier at 102 Kilos vs. 97 Kilos "
Both are the same height at both seat and bars.
It is surprising how much beefier the Mk2 feels next to the M8 looking at those #'s, but the Mk 2 definitely feels bigger.
I am 5'6 155 and the smaller bike fits me like a glove.
PSchrauber has good reason to have issues with the Metralla as despite the simple design they can be finicky.
I have been chasing small problems since I got it.
I would not feel comfortable riding a long way on it not only for the mechanical/electrical gremlins but because they vibrate like crazy.
You need to keep the torque wrench ready and the story goes that with the Mk2 you had to carry a pocketful of plugs and tail lights.
But I love it none the less.