G'day folks,
The 2711 certainly had a 11 Series Briggs - but not the I/C specification.
Note the up-market air cleaner cover and muffler guard used on the I/C version.
IIRC that muffler is the quieter/larger 'Lo-tone' version as well, so probably an upgrade from the standard type.
As with the standard 11 series as fitted by Rover, the air cleaner under that chrome cover is a dual element version. Cylindrical paper cartridge with oiled foam sleeve pre-filter.