Jac,
A significant number of Scots Presbyterians fled to Ireland in the 1680s. The period was known as the killing times. Your problem is that there are few records in Ireland for the 1700s, and so tracing the family in Tyrone will be very challenging and perhaps impossible, especially so as the families evidently only lived in Ireland for 60 or 70 years.
They will have attended the Presbyterian church. Covenanters in Ireland today are generally called Reformed Presbyterians but they didn’t have any Ministers in Ireland till 1757 (when Rev William Martin was ordained). So apart from occasional visits by itinerant Covenanter Ministers from Scotland (who left no written records) your ancestors would surely have attended the mainstream Presbyterian church. However I do not know of a single Presbyterian church in Tyrone with any records for the period 1700 – 1750. And there are few other records to research either, especially if you have no idea of where in the county they lived.
The 1901 census of Ireland contains 192 Wallaces in Co Tyrone. Most of those were Presbyterian or Church of Ireland with a couple of Catholic families, and some Methodists (who would have been Church of Ireland pre 1816). You could use that as a crude method of trying to narrow the search area but with the passage of 150 years since your families left, it may not be all that reliable.
http://www.census.nationalarchives.ie/search/
Possibly DNA testing may be a way of matching with others who have additional information about where the families resided in Ireland. Family Tree DNA reportedly has more people with Ulster roots than any other company. That obviously increases the chances of finding a match. You might want to try them or, if you have already tested, you can transfer your results to them for no fee.
The North of Ireland Family History Society is running an Ulster DNA project in conjunction with FTDNA and can offer testing kits at a reduced price. http://www.nifhs.org (Go to DNA project on the website).
