Hi,
I'm about to fit a cast iron fireplace into a chimney breast which
originally was used for that purpose so the dimensions seem ok. I've
bought a secondhand reproduction cast iron fireplace (one with tiled
insert) and a seperate wooden surround.
To fit, do I simply place the metal insert into the opening and place
the wooden surround over it and screw the surround to the wall?
Or do I actually need to chip away some of the plaster and set the
edges of the cast iron insert back a fraction in the wall and plaster
in place?
I've read of people using fire rope to stop smoke escaping through the
sides, but I'm not sure if this is required.
I realise I will have to backfill with rubble and mortar and top off
with fire cement but I'm just not sure what exactly secures the insert
in place if you know what I mean?

The fireplace will be used occasionally to burn solid fuel. The chimney
has been cleaned and checked.