I have to say that if Father Devitt couldn?t locate the family in 1848, it will be tricky enough for anyone to find them now.
With regard to the townland name, Meamnachrevan etc, townlands often had several names and spelling was rarely consistent and so these differences are not very unusual. Griffiths Valuation (1848 -1864) sought to bring some standardization to them but prior to that there were many variations. It?s probably safe to say that it was somewhere in Templecrone parish. Perhaps someone with local knowledge may be able to assist.
The tithe applotment records (1828) will give you a list of townland names in Templecrone at that time. (Use the Browse facility and search under Donegal/Templecrone). You?ll see that there?s a load with question marks against them suggesting that the authorities have struggled to compile a comprehensive accurate list.
Boyle is a very common surname in the area and the parish records (RC parish of Lettremacaward) don?t start till 1876 so there won?t be any help there.