Hi Tony,
I went to Perth library and had another look at the Pre-1855 Monumental Inscriptions for Perthshire.
This was written by a couple of the name Mitchell in 1974.
They are the ones who divided the cemetery into 6 blocks with the 7th Block G being the wall surrounding the cemetery.
By reading their instructions I was able to ascertain where the headstone that Peter Haggart bought should be.
It was number 178 and was on or near the west wall.
The next number 179 was on or near the south wall, much defaced.
I think it is safe to assume that stone 178 was on or near the west wall close to the south wall.
Also in the Library is a book written by a guy called William Sievwright in 1893 titled
Greyfriars Burying-Ground: Epitaphs and InscriptionsHe also wrote a supplement in 1895.
It was in that book that I found these:
Peter HaggartPlaced by Peter Haggart and his Aunt Jane Campbell In memory of her mother Grace Stewart,
who died 24th July, 1841 aged 82 years.Robert HaggartPlaced by Robert Haggart in memory of his spouse Helen Garvie, who died 13th April, 1834, aged 55 years.
Also George Haggart his son, died 6th March, 1846, aged 35 years. Revised Mary Kemp.This is the south-west corner of Greyfriars.
As you can see there are almost no tombstones here.
By my reckoning Peter Haggart's stone should be on the ground between the south wall and the large stone attached to the west wall.

The two slabs at the south wall are completely covered with moss.

The grassy border between the wall and pathway had numerous headstones in years gone by.
It is my belief that headstones were removed so that it would be easier to cut the grass.
