Possible Clues:

• Serious archaeologists perhaps employed in the dead centre of Glasnevin
• Serious Australians, perhaps, those preparing resting place
• Serious machinery on the farm put to work in the dead centre of Glasnevin
• They break new ground of late for those making way for half of 26 across
• Serious Aussies who may work alongside the church
• They're always putting down the first four figures in 1 across and they work those at rest into the ground