OM603 Ring Gear Tooth Count

[Dannydangles]

I wanted to install a tach for testing purposes into my project, OM603 swapped into a 92 Sierra. I purchased a small/cheap unit that apparently can use a mag pick up, only requiring the correct amount of teeth on the ring gear to be input as a parameter. I read somewhere that the om603 had a 144 tooth ring gear, is that correct? During testing the tach seems correct at idle 650rpm ish but reads low at higher rpm.

Engine is out of an 87' 300TD

Thank you

Dan