hunter rpm gauge

Hello

I am a forum newbie and have been browsing a well known auction site for aircraft gauges etc – I have acquired a Hunter rpm signal general and now if I can only find the appropriate rpm gauge. Would anyone happen to know what type of gauge would most likely have been installed – Smiths seem to have made a whole variety of gauges – 6A/6680-99-4338671 for example or an 6A/6381 – lots of different Smiths reference numbers – I am optimistically going to try and make it work –

Many thanks