US auto makers had mixed vehicles for years. Crazy to have to have both types of tools on hand.
It's your call. Do you want to discard it the first time it breaks, or fix it? If it's 40 years old, it's going to require inch sockets.
There are LOTS of machine tools left over from WW2. Lathes, mills, shapers. Companies bought them, surplus, for pennies on the dollar. They still work, hold tolerances.
Fix them, or junk them because some bureaucrats in Brussels was raised with millimeters and couldn't convert from one system to another at gunpoint?