Problem is, I don't know how accurate my frequency generator is. If I knew it was spot on, i'd probably be willing to do a few for a small fee. Let me see if i can find some means to verify.
I have a cheap frequency generator that is most likely the same guts as yours, just different box. I checked it with my DSO Nano V3 and it was spot on:
I checked my 93 tach and surprisingly it was not that far off f ett om the factory. After messing with the pots for about 20 minutes and going up and the the scale a few times, I was able to get it almost perfect!
The difference of 25 is essentially the width of the needle.