speedometer face plate replacement.

piel off the chrome trim from the gauge , whit a small fork you can lift up the needle , be aware of the position , than you can replace the face plate.

I heard it is easier to leverage off (bend out) the tabs around the bezel if you tighten an appropriate size hose clamp around to reduce flexing….

Rocky

...and after that, not so hard to get things back in place...the hard part is trusting the speedo (!)

   - The pointer just yanks off.  Or, I mean, very gently pulls off... suggest placing a thick paper between your hands and the dial face and/or wear rubber gloves to avoid leaving handprints on the dial face.

  - then just 2 screws to detach the face.

  - then, move the alternator/brights/turn signal 'jewels' from the old face to the new. Just use Veglia assembly tape (aka clear packing tape) to hold these in place on the rear face of the new dial...

-assembly is the reverse of dis-assembly...

  which reminds be that before you do any of that: remove and install the bezel with the face of the instrument held down to the table top with a clamp. put a thin towel on the table, then put the gauge face down on the table,  and then secure it with a big C-clamp to the table. Then apply the 5" pipe clamp around the bezel to keep it from being deformed as you bend back (what are probably just tabs, not the whole of the bezel as with the 2" gauges). The clamp to the table will keep all this honest, it will avoid bending the bezel (and the bezel is the single hardest thing to replace...you will only find another one in a used Veglia gauge, the size is not common with anything other).

Of course, when you are finished the Odometer will still report Miles, and you can just hope and pray that you placed the needle even close to a true speed indication. This is where a professional would used a calibrated motor that spins the proper speed (1600 turns/mile, for 60mph/100km? and was adjusted for your tires, and just budge the needle. Otherwise, before you put the glass on, you'll need somewhat to hold the speedo and have a patient wife to drive her car at 60mph reference or click the stopwatch between mile markers...

And on top of this, my assumption is that the "stop" (the pin around 10mph) also aligns with the 'rest' condition of the movement, and if not, well, the movement needed to come out of the can there are step 2 so you can hold the movement while positioning the needle...I'll say I solved this problem by paying $250 for a professional to do the whole thing, but who knows if my tire choice will ever make the speedo more than just a relative indication that the car is really moving... Lee

FWIW, if you have such a problem, the DeTomaso Mangusta and- I suspect- the Longchamp & Deauville speedo all use identical instruments, which adds a quite few more to the potential pool of spare parts. Those last are more common in Europe thus have metric dials. What differs is- as was mentioned- the cable drive parts. But there are mechanical converters for sale.