UPDATE
I think I have managed to solve this kind of. I changed the Product assignment to SAP NETWEAVER 04 and chose Process Integration (PI/XI) as relevant assigning the Java stack XID as Techincal system.
This then at least gave me the option in MOPZ to upgrade the system to SAP NETWEAVER 7.3 or SAP EHP1 FOR SAP NETWEAVER 7.3.
Seems that MOPZ or something really didn't like the Product assignment of SAP EXCHANGEINFRASTRUCTURE 3.0.
Cheers
Craig