Yeah Mick, the combustion chambers are much deeper, but they need to be matched to the bore size, so if the cylinders are bored out to 65mm, the combustion chambers need to be "relieved", or milled out, to 65 mm for the first couple of mm.
Just trace the outline of the cylinders (using the new 836cc head gasket as a template) over the combustion chambers, and mill them out accordingly. Cheers, Terry.