Hi Sandie,
Am ever so glad to be receiving messages about your search for Leysborough near Aghabog. I wish you success.
I think your message may have come as a result to some degree or other of my original request for help searching for information on my Niblocks in the Listroar and Corlongford area southwest of Clontibret. Unfortunately, I am just as stuck now in regard to getting further back in time than 11 Feb 1795.
Your request prompted me to return to searching for anything that might be helpful to you.
Initially, that took me to the Drumallan area to the northeast of Newbliss, to the area of Drumullan and a lake known nowadays as Amagose Lough AND to an area east southeast of Newbliss and a lake known as Feagh Lough. Nearby Feagh Lough, I see on Google Maps referencees to Corlougharoo Stud and Patrick J. McGuirk and Tyrone Guthrie Centre (because of its proximity to Annaghmakerug Lough). Addresses and other contactt information to those three places are fairly easy to find, some actually on Google Maps.
[In the preceding paragraph, you see the search terms in my line of focus: Aghabog, Drum, large lakes (Amagose Lough, Feagh Lough, Drumate Lough, Annaghmakerug Lough and Long Lough)]
Then, I looked for Drum and found it, some ?6 miles south of Newbliss and a nearby lake there known as Long Lough - which might be the same Long Lake you speak of in your recent inquiry. In that Drum area, I found references to at least four people who should not be to difficult to locate and contact. Primarily, I refer to Mervyn Reilly (Worshipful Master of Aughareagh LOL 1555. I also found https://www.facebook.com/DrumAccordianBand which might give you direct and quick access to further informationn about the Drum area.
At https://www.irishtimes.com/news/ireland/irish-news/protestant-drum-is-still-beating-strong-in-border-village-1.2748306 AND https://www.belfasttelegraph.co.uk/news/republic-of-ireland/welcome-to-d... you will see referencess to this Mervyn Reilly and at least his musical activities in and around the area of Drum. With that Facebook URL, you should be able to contact Mervyn (or others) who might be able to help you in your research.
Other than this, I doubt I can be of any assistance to you in your search down your anbcestral traills to William (Francis) Ley of Leysborough. But I have tried! That is because I have no first-hand knowledge of genealogy-related skills applicable to this area of County Monaghan. In fact, I live nearly 7142 km / 4438 statute miles to the southwest of that area, on an island in the northeast Pacific Ocean. As my first and heretofore only post on this website indicated, I was and am still very interested in my Niblocks in the Listroar and Corlongford area southwest of Clontibret. They, too, left Ireland in late December 1848 or very early in January 1849 and, via Liverpool, arrived in New York City on 24 Jan 1849 on the sailing vessel "New World".
One additional thought: might your "William (Francis) Ley of Leysborough, Monaghan, married to Eiza Lucas (William and Mary Lucas)" be related in any way to the Lucas Family dynasty referred to in . . .
https://en.wikipedia.org/wiki/Castleshane,_County_Monaghan? Is it just concidence or is it more, that the names of Francis and Lucas are also a central part of the Lucas Family dynasty and their seminal influence in the Castleshane area (some 6 km / 3+ miles east southeast of Monaghan City?:
"Francis Lucas, eldest son of Henry Lucas and his second wife Alyce Bradocke. Francis was born circa 1553. His descendants held Castle Shane (spelled as two separate words), the country house on the Castle Shane Estate, for many generations. The original castle on the site may have been late medieval.
However, the castle was largely rebuilt for Francis Lucas, probably in the late Elizabethan style, around 1591," but ruins of the original building might still be seen near Castleshane.
Finally, the Clogher Historical Society (Cumann Seanchais Chlochair) might be a useful contact for you. At least one of the people listed on their website has been very earnest in trying to help me in my research into the Niblocks in the Listroar and Corlongford area southwest of Clontibret. SEE http://www.clogherhistory.ie/index.html
I'll stay alert for further information and your eventual success in your search.
John