It looks to me like the hole is pointing upwards to the tailshaft, not horizontally underneath the tailshaft, is that correct?
While it may have a worm gear on the shaft, the fact that the hole points directly at the tailshaft means you can't get the other gear to mesh with it. Worm gear setups can't have the shafts in the same plane.
Camaros and S10's have the speedo located in different spots. To get the speedo to work correctly when putting an S10 tailhousing on the Camaro tranny, you need to either swap out the tailshaft, or modify the Camaro tailshaft to accept the new gear location. Look at the tech tips section on the left sidebar, or contact Tony P for more info. He has posted some good photos and info on doing this on the HAMB a while back.
I'm guessing that somebody put this all together and realized they screwed up, so rather than swap out the tailhousing, they pawned it off onto you. If you get the correct tailhousing for the mech sender, then you will be fine, assuming the gear was installed correctly onto the tailshaft.
