Hey barbee6043,
I'm thinking the Ford F-150 pickup uses the same vent tube fitting.
See here for details.
Cheers!
https://www.lmctruck.com/1973-79-ford/drivetrain/fc-1973-79-rear-axle-breather-vent
EDIT : Just re-read your post and I now see what you are trying to do.
I would see if you can get a helicoil with a 1 " outside diameter and a 7/16 inside diameter. Then , you could use the smaller fittings.