There are 3 different speedo drives that work with 16" FL wheels.
One has a .440" spacer another has a .375" spacer and the last has no spacer on it at all.
I think you need the third one and add your own spacer.


If you look through the aftermarket books you need the 2240:60 ratio.
It is right around 2.75 revolutions.


Have you checked to make sure the wheel bearing race is fully seated inside the wheel?

 

Ok I just went and looked in the Drag Specialties book and it has a speedo drive unit I think you can use.
It is part number DS-243859 which replaces OEM part number 67073-81.
It is a 2:1 speedo drive so I'm not real sure it will give you an accurate reading.
Your other option us take a grinder and grind down the spacer on the speedo drive unit that you have until it fits into the wheel.

 

Thank you. I will take a look at it.