I tried researching this the past two days, and it's been a little complex with not a lot of info on the internet. From what I've found, it appears the plants were often in flux, with changing roles over the years. Sometimes stamping operations, sometimes body assembly, sometimes hardware, interior, etc. Also, some seemed to have been referred to by various names - sometimes the nearest big town, sometimes the actual town, sometimes the county, sometimes the street location, and the oldest Fisher plants in Flint and Detroit even went by numbers. My best guess as to the Fisher stamping plants at the time is:
*Wyoming, MI - 36th & Buchanan
*Grand Blanc, MI - South Saginaw Street
*Flint, MI - Bristol Road, sometimes referred to as Genesee (County), appears a tool & die plant was also in Flint
*Grand Rapids, MI - Alpine Avenue
*Kalamazoo, MI - Comstock Township
*Mansfield/Ontario, OH - West 4th Street0
*Hamilton/Fairfield, OH - Route 4
*Cleveland/Coit Road, OH (not sure what the did in 1966-1969)
*Marion, IN - West 2nd Street
*Chicago/Willow Springs, IL
*Pittsburgh/McKeesport, PA (aka West Mifflin, PA)
It appears a good number of these plant are abandoned, demolished, or repurposed today, with stamping operations now moved to other locations.
The T code is still a mystery. The only Fisher plant I ran across with an obvious T in the location/name was Trenton, NJ. But it appears that plant made hardware and smaller parts.