4000 ppm to speedo lt1 94

[honken]

Its a 350 lt1 from corvette c4 1994 and pcm 16181333.
I installed it in my el camino ss 1970 for 10 years ago.
Bought aftermarket tacho and speedo (china) , the old was from a van .
Trying to program the speedo from pcm output.

Tire rev/gear ratio= tail shaft revs.
4000 ppm/tail shaft revs= pulses per revolution (ppr).
Tire revs*ppr/60=???.
speedo frequecy/???= the value for speedo (on my speedo),