I checked the suburban directory for Pittsford NY (which is where 3500 East Ave. actually is). It is a restaurant and has been at least since 1930. So someone dying there isn't correct. There is the Rochester Friendly Home at 3156 East Ave which is a type of nursing home. The Rochester Library Life Records page has an index entry: CLARK, MARY O'CONNELL. died 7/13/1970 notice in TU 7/14/1970. Wills are at the County Surrogate Court, but there is a proviso: from [http://mcnygenealogy.com/resource.htm
Research rates: By mail - $90 per search and 25¢ per copy. In person - search for free and paper copies are 25 cents (film copies $1).
The LDS Family History Library has filmed the index to all Surrogate Court records through 1970 and they also filmed the wills from 1821 - 1901 but they did not film the entire file. Search for available records at the Family Search website.
Have you determined if the couple lived in Rochester or elsewhere?