Electric Speedo Help

After adding in 3 autometer gauges, the speedo isn't working, also the speedo gear got chewed up in the tranny, so I figure I'll order a programable speedo. I need a white faced gauge but am not sure if the 3 3/8 or 5" one is the right size. since I'm hoping it will slip right in place of the old I'm thinking it's the 3 3/8"? Any ideas as to which one & I assume I need a sender as well? Are the senders easy to install?

I have a TCI C4. Since there is a speedo cable now, I assume I don't have a vss. Maybe I need more than just the sender from autometer? Doen't sound like many people have tried this since no other responses. I try to call autometer again. I was already on hold for 20 minutes before hanging up.

thanks for the reply