I am looking at electronic instruments for my bike as well.
I will be running a modified front hub without option for the speedo gearbox, so i need another solution.
Given i am there, i was then thinking to couple it with a rev counter as well.
While searching for one i understood that the Smiths trade mark is not really protected, but the ideal continuity of production is with Caerbont Automotive Instruments :
https://www.caigauge.com/
(read their Q&A page and this quote from Wikipedia
https://en.wikipedia.org/wiki/Smiths_Group :
Clocks, watches, and automotive instruments eventually ceased to be significant markets for Smiths,[11] and by the 1980s, the automotive instrument division had been sold,[11] first to Lucas, and eventually to the factory employees. The new company, Caerbont Automotive Instruments, continues to produce classic Smiths-branded instruments with the blessing of Smiths Group plc.[20] )
And they produce indeed a Smiths classic motorcycle range:
https://www.smiths-instruments.co.uk/bikes
I have inquired for a rev counter and they quoted me 230 GBP (last year).
They also can provide the sender unit both for the wheel for the speedometer and for the coil for the rev counter.
The instrument can be set to tick as the original cronometrics.
The only problem is that the case measure 82x44 mm instead of 80x 32 as per the original instrument.
Also they have a pressed in bezel instead of a screw in one.
But, there is another company in the UK also making electronic speedos and tachometers. And they do them using the correct 80mm case and screw in bezel:
http://www.puca.co/productC.html
at 234.99 GBP
They also make a 5inches speedo and rev counters for the Vincent:
http://www.puca.co/product5C2.html
For their instruments they use CAI internals or some german made ones.
They claim their instruments to be more faithful to the original design.
Best,
Edmondo