Hi,
I don't have such problems on Windows 2012 R2 Server with installation of Workflow Server 7.6 release.
First it said that I don't have a IIS 6 Compatibility installed, after that I've installed it and next attempt of WorkFlow Server 7.6 installation didn't throw any messages about IIIS, etc.
Here is what I have in Server Roles and IIS AppPool
Thanks,
IP.