I had not considered you might have a nacelle (BSA type) but if thats the case, and you are on a budget then at that price point (And assuming you can get a cable to fit) then I would consider rolling the dice on one of the Indian ones.
I have a friend in India and he claims he was the leading manufacturer of replica instruments and some years back others noticed he was successful and started making their own. He gave up on making them as the market got flooded so my belief is its just hard to figure out which are a decent quality and which are not.
But as I said, and failed to properly illustrate, is that some really nice looking (And performing) replicas are being made now. I have a grey face and a black face set somewhere in storage still in boxs I bought for some projects where original is not important. I get them wholesale and am not going to post the prices here but the retail on them is very affordable and like I said, I sell a fair number of them over the years and no complaints. The ones on the Triumph I took a picture of were an earlier version and those were fitted about 10 years ago and were owned by an old guy who puttered about but not extensive mileage (I bought the bike back from him when his health was failing)
Here is a picture of the current repops,, I understand there is some with a Chrono style face but internally are magnetic. See:
http://jrcengineering.com/product/ssm500106/This is the tacho (Again grey face) See:
http://jrcengineering.com/product/rsm300301/I rarely deal with the public as a shop anymore (No thank you!
) But I still have most of my dealer accts. So, seeing as you are in the UK I dont think its practical to try and peddle you any parts, and these are readily available thru a variety of UK based dealers.
But as a shop it used to annoy the heck out of me how many calls I used to get asking for "A decent used set of instruments" or "Used speedo drive". Nobody wanted to pay the cost of new replacements and so when these replicas came out, It was a good option for those who did not want to pay the cost for new or rebuilt originals. Lots of people wanted to swap out their rusty rims for a "Nice used set with good chrome" as well.
So Cheap Basta........ Oops, I mean economy conscious consumers I feel your pain but
it made it hard to run a business.
heres a set on US ebay of Chrono replicas (Speedo and tach) and if fitted in some sort of cups they look pretty good but as I said, from the side or back they look like cheap knock offs..(but for a bitsa custom who cares if you can cover up the ugly part?) These are located IN the UK --seller
See:
https://www.ebay.com/itm/Matching-Chronometric-120-Mph-Speedometer-And-Revcounter-Smiths-Replica-Items/112515524760?hash=item1a3272a898:g:aIUAAOSwtPhZiYr0&vxp=mtr