[rsk289]

Sorry Glen, your photo won't appear (blue box with question mark), but I can tell you that the correct ammeter for a leafspring car is a Lucas BM4. It doesn't match the other Smiths instruments, and is a 30-0-30 instrument with a pendulum needle shaped like an arrow. It has a full printed scale but no part number visible on the face.
'BM' stands for 'Bakelite Moulded', or maybe 'Base (or Back) Moulded', borne out by the screw terminals on the back being set in the moulded bakelite casing. There is no screw post for a clamp as the ammeter is a push fit in the dash, with small tangs on the chrome bezel to help retain it. It relies on illumination coming from the external bulb on the fuel gauge and has no bulb of its own.

Roger