[Vwpickups] Speedometer repair possibilities

[ken1]

I have a speedometer on my 82 pickup that is malfunctioning, the gears are either stripped and/or broken, cause the speedo hub will not turn.
The number on the face is 1575. I have heard that the number has something to do with the percentage of error when running???. 
I have access to two (2) speedos from parts clusters. One has a number of 950 and the other is 1540. Neither is an exact replacement for mine. There is a hump on top of mine that would hold  a EGR light and a oxygen sensor light, but the slots are not used. But the shape of the speedo causes the holes to not line up properly. Is it possible to use either the speedometer(s) or at least some of the parts to get mine working?
Thanks.
ken