Speedo gearing again, XK140

My 140 originally did not have overdrive, and was built with a 3.54 rear axle.
I have now fitted a JLE box with overdrive, and am getting around 10% under read on the speedo. The angle drive for the speedo is a new one, but the speedo in the car is a X51691/41 1280. It was pretty dirty and had obviously been in a car for 77,000 miles - but I’m wondering if it started in this car. According to Viart/Payne, this speedo was fitted in cars with 3.77 axles, not 3.54 as my car has. The ratio I have should be used with a X51691/35 1200 speedo. Could the one I have be right, or is it more likely to be a replacement at some point? It seems odd that it should be correct for a 140 if that’s the case.

Hi Roger…assuming Viart is correct…have you checked the parts catalogue…i doubt very much it left the factory with an incorrect speedo…but i suppose anything is possible…but more likely a replacement…Steve

Parts book, good idea.
Incidentally I’m assuming the needle ‘blunt end’ should be black. 140 Explored shows them as white, mostly, although it varies.