Yes, the brake master cylinder is also used on the Giulietta.
The brass sleeve is best explained by taking a small detour: Brake fluid attracts moisture. The moisture condensates and, because it is heavier than brake fluid, typically accumulates at the lowest points in the brake system (e.g. at the bottom of master and slave cylinders) where it starts to corrode and pit the bodies, which eventually leads to leaking cylinders that cannot be fixed by using a new kit. At that point, there are two options: (1) replace the cylinder or (2) drill it out and use an insert that provides a clean and unpitted surface for the pistons and seals. For the 2nd option, brass which is machined and inserted as a sleeve. You'll need to ask around who could do this for you.
BTW, I was told "spun" brass with metallurgical grain that is circular (and therefore perpendicular to the piston action) is better than extruded brass with longitudinal grain -- however, this difference is probably less important than having proper, circular dimensions and roundness.