They're not all of the same family at all,actually.
The GPz range are all air cooled and thus are 'family'.
Although the bastard offspring GPz305 twin can technically be excluded.
The GPZ models such as the aforementioned GPZ1000RX and the seminal GPZ900R are liquid cooled and of a totally different design throughout.
It's all in the zed,baby.
Yawn! Anyway I don't think the (Z or possibly ZX) 750E Turbo was ever sold as a GPz/Z in the UK, it had GPZ stickers on the engine but thats about it.