Early e40d speedometer setup

Ive got an 89 bricknose with the e40d its 2wd and setup with a speedometer cable. The vss and and cable are located in the tailhousing of the trans. The issue started with no speedometer on the dash and the trans shifting like crap. so i pulled the cable from the trans spun it to see if the gauge worked and it did. I then felt inside the trans for a gear on the shaft and there was nothing. So i pulled the tailhousing and there was nothing on the shaft indicating a gear. My question is how were these setup was it a plastic gear that clipped on like the c6 trans? or was it made to the shaft and this trans has been swapped? I just got this truck and this setup is all new to me im used to the electronic setup on newer trucks.

Well ive found out going through some old manuals that the tailshafts on these trucks were machined with the drive gear in them so other than swapping a output shaft im gonna need a new trans or swap to the psom digital setup off a newer truck does anyone have info about this i have 2 parts trucks what all would i need to do