Yes that is true. But I can tell you right now that all the factory stock 1964 1/2, 1965 or 1966 Mustangs with a 170 or 200 Six all came with a 2.77 Manual Transmission these will also al have a 8 1/2 inch Clutch Assembly with the Dog Dish Stepped Flywheel.
Note that if yours has the Original 1966 Engine Block (these would have the Dual Bell Housing Bolt Patterns you can check your Blocks Casting / Design Numbers to verify this it should be a C6DE-6090- Number). In that case then you would have the ability to swap to the 9 inch Clutch and use the stronger and excellent shifting 3.03 Trans but you would need to change everything from the back of the Block. The 1967 Six larger Bell Housing, its matching Block Spacer Plate, the larger Flat Flywheel, the bigger 9 Inch Clutch, 1967 Clutch Release Bearing, 67 Clutch Release Arm, plus the Starter to a 2 bolt, the much better 3.03 Trans, Shifting Linkage, Some Clutch Linkage, Drive Shaft Yoke, Etc. it would all bolt right in. Good luck