I just went to add the block to my communities forum and it wasn't listed under 'pages'. Has this changed in 4.1 or is it a bug?

I still have it showing another site that I upgraded from 4.0 to 4.1.

If a widget is missing in the sidebar of the block manager, it suggests that it is already in use. Some widgets can be used several times, some just once. 
But for record feeds, you can alway create custom feeds in the ACP and then add them instead of the default feed widget.