Hi Hubery,
Is your 7.4 system, Dual-stack or single-stack? And in 7.5, you do not have ideal dual stack option.
If you want to have dual-stack option in 7.5, then you need to go for dual-stack split option. Below link for dual-stack split -
Also more information about SAP Netweaver discontinues dual stack installation -
SAP NetWeaver Discontinues Dual Stack
If you are upgrading, then it must be SAP PI 7.1 to SAP PI 7.4 dual stack.
REST adapter is available from PI 7.31 SP14/ PI 7.4 SP 09.
Regards,
Nitin