The South Hadley History Room at the South Hadley Library is a valuable resource to do local history and to do genealogy.
They have book, maps, and internet resources.
The South Hadley High School yearbook – Gateway – collection is from 1947 to the present.

The Gridley Canney Collection
South Hadley Town Reports from 1889 to the present.

There are Street Listing by Wards and Streets from 1929 to the present.

Holyoke City Directories with South Hadley from 1884 to the 1990s

Fire District Reports

Municipal Light Board SHELD reports 1949 to the present

The Spotlight 1929 to 1936
South Hadley Phone Books
Know Your Town 1947 onward
Congregational Church of South Hadley Falls
Nice map collection

Books
In Old South Hadley by Eastman
Geology of Old Hampshire County by Emerson
County Atlas of Hampshire (Massachusetts state book) – click to get PDF
The Power of Christian Benevolence by Hitchcock
Some Old Time Meeting Houses of the Connecticut Valley by Wight
The Old South Hadley Burial Ground 1976

Holyoke in the Great War

Hampshire County Gazetteer

I have an uncle who was listed in the city directory in the fifties as a stationary fireman. He may have been working in the boiler room for a plastics coating company. Do you have any idea what the company would have been?
The Plastics Coating Company existed in Holyoke and in South Hadley during the 1950s and the 1960s. Your uncle would have shoveled coal into a heat furnace.