Greeting from Eaton County, Michigan
I have the some of the answers to your questions. I look for area directories when I go to flea markets. I have a directory for Eaton County from 1966 before the Zip Codes. Rural Route one in northeast area from Charlotte towards Potterville.
The 1st road is Benton Rd from the Charlotte city limits north and ends at Vermontville Hwy.
The 2nd road is Kinsel Hwy from North Cochran going east to Benton Rd.
Number 3 is Fairview Hwy going east from Benton road to Otto Rd.
Next is Otto Rd going north from Packard Hwy maybe to Vermontville Hwy.( this is not specfic enough in the directory)
The last one is Lansing Rd(not I-69 as it was built I think in the late 1960's.)The old lansing Rd is still there.It does go all the way to the Potterville city limits as my sister lives there.
As far a phone numbers try the Eaton County Genegealogical Society. The society has phone directories from 1920's.
The do have a web site. Good Luck! Janet