The device has a few different names depending on where in the world one is/who made it, etc. I call it a
Brake Pressure Differential Valve or BPDV. The manufacturer, ATE, calls it a Differential Pressure Warning switch (DPW).
From memory, all the lines and the two brake light switches on the front use a 10mm x 1.0mm thread. The switch on top is, I think, 12mm x something. The lines use a standard ISO bubble flare.
Your BPDV is unique in that it has three switches and was used for the 1969 model year only; all USA Alfas 1971 and up have only the single switch on top like yours does. The single switch on top of all BPDVs, when activated by the BPDV upon detecting a hydraulic pressure loss in one of the two brake circuits, provides the ground circuit for the brake failure warning light on the dash. The 1969 BPDV also provides a convenient location for the two hydraulically activated brake light switches. Although activated by hydraulics, the device serves no hydraulic purpose whatsoever.
The brake light switches are available new from your favorite Alfa vendor and the switch on top is available through Porsche (can provide the part number if you need it).
The BPDVs are not available new but I've rebuilt a number of them over the years and would be happy to assist you.