It's important to distinguish between language versions and platform versions... and likewise functionality. Currently you're mixing up various aspects.
Func
and Action
aren't part of the C# language at all - they're just delegate types which are part of the .NET framework. If you're using a version of the framework which doesn't include the delegate types you want, just declare your own. I'd suggest naming them differently to the .NET ones so that it won't matter if you then upgrade - there won't be any naming collisions. So:
public delegate void MyAction();
public delegate void MyAction<T>(T input);
... etc
Then once the relevant types are in place, you can use method group conversions as normal:
public void DoSomething(MyAction<string> action) { ... }
public void Foo(string text) { ... }
...
DoSomething(Foo);