The speedo has a trip so its obviously not for a military machine, but they are all the same 2 bolt mounting configuration, the bracket varies depending on the make, model and year so perhaps you will need to say what you are going to fit it too.
I've got the 1949-58 BSA "M" spares list but it only pictures the nacelle, but I suspect the first tele M20 may have used the central mount like the pre war models?
Hopefully someone with more postwar knowledge will step in here.
I mounted one of these speedos on my WM20- 41'.
It works great, but the reading is quite accurate as Km/h,
Although it stated "Miles" on the face of it.
I do have a good original NOS Smiths, but I prefer to keep it safe, at home...
When I tried to install the repro with the original bracket, I could not,
Because (Please note at photos hare)the cable port is eccentric on the Smiths,
Whilst on the Indian repro it is centered, so on the older M20
It clashed with the bracket.
Secondly, the mounting screws on the Smiths are placed vertically,
And on the Indian - horizontally,
So it would probably not be suitable as a direct replacement, but with few
Adjustments, It would probably work.
On the Smiths speedo looking at the face as if using it the mounting studs are at 12 o clock and 6 o clock. On the Indian made ones the studs are at 9 o clock and 3 o clock