You'll likely find varied claims online, but you shouldn't expect to find official EPA numbers easily. Real-world mileage would be highly variable, potentially ranging from low 20s to mid 30s MPG, depending on the factors mentioned above.
To get a better idea of the actual gas mileage, you'd need to look for owner reports on forums dedicated to classic Ford trucks, or search for information specific to that particular model year and engine in used car listings from the time period (if any provide that information).
