There are Mk1, Mk2, Mk3, & Mk3.1 versions of the Churchill 6
MK1 Pre August 2012 has a single top brick ( baffle) which sits in a cut out in the rear bricks.
Mk2 August 2012 - March 2014 has two top Bricks ( one upper, one lower Baffle) and straight rear bricks.
Mk3 March 2014 - October 2018 has a single air control, two small top bricks ( baffles ) supported by a bracket
MK3.1 The glass in this model is 335mm x 318mm. There is no ash pan seal.