Did I mention this is a Metuchen car
I saw it in your signature but don't ahve a collection deep enough and there are much fewer NJ cars due to the run to pull info from
It looks like the style used in a 65 Falcon Sprint http://www.fordmuscleforums.com/attachments/falcon-pages/20435d1325949457-tach-position-sprint005-1.jpg
I checked with the original owner and he never had a reason to change it and neither have I.
Would not be the first owner that forgot something. Have had them tell me and friend tons of things only to find the opposite took place. Not completely their fault its been 50 years and often these were just one of many cars they bought used and got rid of or parked at some point.
My guess is that because Ford stopped Sprint production at the end of 65 due to the Hipo Mustang, Ford probably had extra inventory of these cables from the Falcon to use up but again it's Metuchen so who knows. My car has other left over 65 parts including 9" housing and washer motor so it wouldn't be unheard of for Ford to use up old inventory where possible.
The assembly plants didn't have space to store parts so they might use them later. End of production parts (the few that got to the plant were normally transferred and used as service parts or sold by the shipping crate for salvage some times. Then just write the lose off. Believe the Falcon also used a different mounting bracket
One other question regarding the location under the dash, mine is by the ignition switch and I have seen others located on the left side of the steering column. Is this random or did 4 speed cars get them on the right side to avoid interference with the clutch pedal?
To the left of the steering would have been the normal location - that is why the cable is so long. If your was replaced that would possibly be the reason why (short than the correct/original one) they mounted it to the right. The were routed well away from the clutch and it was likely mounted to the left so you could operate it with the left hand while starting the car with your right hand to the key/ignition. Though later (69) were moved to the left side of the steering column