700R4 change spedo to ecectric from cable

[1-PU70]

I have a 700R4 from a 87 2 wheel drive S10 Blazer in my 70 C/10 with a cable for the spedo. I want to change to an electric spedo. If I change the tail shaft housing with an electric pickup one and pull the plastic gear of the tail shaft do I just press on the new exciter and how do I know where it needs to be on the tail shft. I hope thats prity clear. I want to switch from a cable spedo to a electric spedo.