Hi George,
Not sure what the 147 means.
I reckon that your grandad might lie in the "old" graveyard at Carnmoney.
[This is the one which immediately surrounds the CoI church.]
I have a copy of a map held in the Sexton's cottage.
[Designated as "Survey of Existing Graveyard No.3 Carnmoney Parish Church". Dated June 1961.]
It is marked off in sections, labelled A,B,C,D,E,F.
Section G isn't marked explicitly, but must refer to the remaining area.
If you stood in the road facing the church then section F lies to the immediate right of the church, and section G lies to the right of section F. Both are bounded by the road to the South. Section G is bounded by the internal path to the North.
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There are two ARMSTRONG plots marked.
They are both near to the road.
If you walked along the pavement to the far RHS, then counted off vertical lanes back towards the church ...
... lane 1 (single-width plot);
... lane 5 (triple-width plot; marked AA1 on the map).
Details should be in the "Carved in Stone" book published by NIFHS, or online at "History from Headstones".
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The family will have been granted special "permission" to bury him there because of its historical presence in the graveyard.
[Alternatives would have been the graveyards to the South of the road (one being the euphemistically named "hidden" one), or else Belfast City.]
Formal (methodical) recording of burial locations at Carnmoney only started in the 1960s.
Up till then adhoc methods had been used.
Capt. Jock