This can be done mathematically because you posted all the required info,and it is the best kind of info.
These speedos are adjusted by percentages. since yours is running 13 miles high at 60, I'm gonna assume it reads 73 at 60, and that is 73/60= plus 21.67%
So your speedO pinion gear will need to slow down the needle this same 21.67%.That means it will need more teeth.
Since you currently have a 29 tooth, you will need; 29x 1.2167 =35.3 teeth
But if your speedo reads 60 at 47; then 60/47 =plus 27.7%. And you will need 1.277x29=37 teeth