Yes the boom is different...
Shorter for one thing, but more importantly, there is a hole
at the tail end for the tail gearbox to mount on.
The old boom can be made to work ...
I personally switched to belt drive after being very annoyed with buzzing fins, etc and all my problems went away. So I would definitely recommend it. My Eolo is super smooth now ... I just love it.
Of course this does not mean that the only way to get a smooth running Eolo is to switch to belt drive.... I wish Robbe had released all Eolo/Spirit versions with a belt drive to begin with. It would have made this heli much more successful.
The other thing I like with the belt drive, is that the bevel pinion off of the main gear is eliminated so the front gearbox is a lot easier to setup and turns smoother. Of course there are no bevel gears in the tail either ... Also, the part count of the tail system is greatly reduced and there is a nice place to mount the vertical fin as well.
On the negative side you cannot remove the tail boom without taking off the tail gear box ... (but who cares).