It's indeed the Scarabeo 3. As the original Scarabeo, it has a transverse engine on top of the rear axle, but in this case with an Alfetta De Dion rear suspension, and an angled gearbox. The engine is on the other side compared to the 1966 Scarabeo.
The car was developped by Giuseppe Busso, and indeed the Junior Z body is more a camouflage than an intent to produce an alternative Junior Z.
I has been extensively described by Busso in an article published on Ruoteclassiche, not the reference at hand.