[Alfar7]

The ratios of all are the same. The gear tooth count on earlt 101 5 speeds are different from late models and the 101, 105 series uses smaller syncro dog housing parts than the 115 cars so that will be different.
Some of the bearings can interchange, the rear bearings will not. The later have larger roller bearings than earlier models.

Parts boxes are needed for every era as no dog housings are available new for any of them.
The 115 and Alfetta/Milano share the same syncro parts (not gears)