I live in Co.Sligo. I Know a family with the surname Whiteside.They live in Collooney Co.Sligo. Some of the family I think still live there.This man owned a car business and for many years I bought my cars and had them serviced in his garage. When he died the busines was sold but his sons still live in the area.Mr Whiteside had a business partner who is still in the automobile business in Co.Sligo.I could contact him for you .The Irish 1901 census in on line at theis web site http://www.leitrim-roscommon.com/1901census/census.shtml
The Church of Ireland records in these area should be of help to you. I can get the names of the rectors for you.
If I can be of help contact me at. firstname.lastname@example.org