If lubing the speedometer cable does not fix the problem, the head may be locked up. I had a 40 Ford that I bought with no speedometer cable. I bought the correct cable and lubed it. The speedometer worked for less than a block.
I believe the cable was removed to disguise the fact that the speedometer was not working. SO ... I bought a NOS one from Dennis Carpenter Ford in Charlotte NC. Installed it ( it was pretty
) and it was not any
better than the old locked up one. Sitting on the shelf for 60 plus years was not good for it. Dennis Carpenter offered a refund
but I kept it and sent it off to a speedometer repair service where it was cleaned and lubed. Worked great ... when installed the second time.
Hope the cable lubrication works for you.