Speedo cable length - 420

Hi folks. I have a 1965 3.8S which needs a new speedo cable. The auto transmission however is a BW Model 8 - probably from a 420 or Mark X. Looking at speedo cables on parts sites there is a myriad of lengths and end fittings to choose from. The end fittings I think i can work out but I need to know which length to get and some advice on where it should be routed from dash to transmission. Any help much appreciated. Thanks.

Hi Richard, LHD or RHD?

Left hand drive. I am in the USA.

If your outer cable casing is in good shape, you might pull the inner cable out and measure its length. I would think that Nisonger Instruments in New York could make you up a new inner cable. Back in the 60s and 70s I used to use Palo Alto Speedometer who were able to do this. Not sure if they are still in business now.

My 3.8S is a LHD MOD car and the cable on this car has a angle drive at the overdrive end which is on the right side of the unit, it then runs under the gearbox, and bellhousing and up in a large arc between the block and exhaust (I insulated it for protection) then up and over the heater box into the dash. This may not be stock but it seems to result in the minimum of bends which can cause problems.
You might want to update your info to show your car and location.

Thanks John. The cable that I have is the original for the DG250 box and it is not compatible with the Model 8 box. . It is only attached at the speedo end. I think I will just assume that a replacement needs to be the same length or a little longer.