5-speed speedo pinion

[PineClone]

I swapped out my '78 b210 auto tranny with a 5-speed. The speedometer is way off. There are 21 teeth on the pinion gear from the auto. The pinion gear on the 5-speed is much smaller (i didn't count the teeth). 

 

The gear is molded on the pinion and removing and swapping the two isn't an option (i tried). Swapping out the entire pinion isn't an option because 5-speed pinion is much longer in length than the auto. 

 

There is a good discussion linked here that lists the part numbers...but i'm not seeing many options for the 63A. Before i start experimenting, i'm wanted to check here to see if anyone has done this successfully.

 

Thanks.