The 'anti-clockwise spiral' sequence of progressively loosening and tightening the nuts:

Note that in the drawing above the operator is standing at the carb-side of the engine, whereas in my case I have more space on the alternator side so choose to do top-work from there, in which case this may help:

Three extra nuts 1, 7 and 8 (and modified sequence) under the the rocker shaft on a 1500cc B-series Diesel: (Dave O'Neil)

An original copper gasket copper side ...

... and 'steel' side:

'Front' (left), 'MADE IN ENGLAND' and 'TOP' (centre) and '1800cc' (right) stampings very clear:

Payen top ...

... and bottom - almost identical except for 'gold' wedges between each pair of cylinders on the top and larger 'silver areas underneath:

'FRONT' and 'TOP' markings smaller and less distinct and you have to look closely and carefully. However it has the same 'stepped' front edge and curved rear edge (arrowed) as the copper:

The indicated rocker pedestal nuts can be removed if required without affecting the cylinder head or gasket: