Could be off a Vincent ser B or even earlier,as the big speedo was an extra cost option.Matchless 650 csr s had a 150 mph speedo also,maybe a Jaeger for a foreign market.Of course this Smiths gear was available over the counter,and in the seventies local v8 race boats allways used chronometric tachos despite the high cost.So someone may have bought this for a race car,or bike.Regards John.