All V2 gearbox JGs have a ported cylinder, even the longer ones that should not.
Look at this video at about 20minute mark.
You will see the cylinder has a port, and a small cut out at the rear. That is because the gearbox casing has a small lug that goes into the cylinder cutout to stop it turning I assume.
The gearbox material is soft enough that it will only take a few minutes to file it off then you can drop in any cylinder.
Hope that helps