Never having owned a Ford newer than 1956 ... I cannot say for certain ... but on the numerous 56 Ford F-100's I have ovned ... the speedometer hooked to the GM transmissions ... just like a factory Ford ... bolt on.
Even if their is a problem ... most good speedometer shops can make a speedometer cable up that will work.
I would just check to see if it just screwed on.
There is a strong possibility that the reason it is not hooked up is because the speedometer is way off ... with the speedometer gears in the Turbo 400
(Shown above is a 700R4 ) but a Turbo 400 uses the same type set up. Changing them to the correct ones for your application is not a big deal.