Margie,
I am curious about your source of the information for the marriage. You say it was at the 1st Presbyterian church in Belfast. However there isn’t actually a church of that exact name in Belfast. Also if Eliza Ann’s father was a farmer, you might expect her to have married in a rural area, rather than in a city. (Tradition was to marry in the bride's church).
"Meeting House" is a term often used by Presbyterians to describe their church.
I wonder if the marriage might in fact have been at the 1st Presbyterian church in Antrim town? If so, Griffiths Valuation lists a Malcolm Fleming who lived in Townparks townland, in Antrim town in the 1860s. He rented some land and could well have been a nurseryman. (Much of that area was nurseries at that time. It’s a modern housing estate today though).
James Kerr is a more common name and there are several possibilities in Griffiths. However before researching further I’d like to try and nail down the correct location for the marriage. What’s the source of this information?