There is no sending unit for the Tach and it doesn't hook or connect to the flywheel!

It get's its readings from the coil and is very simple to hook-up.

As far as lockers - what rear differential do you have?

You can install "lunch box" lockers which are the easiest and the cheapest. They can be installed, normally, without having to remove the carrier.

A better solution is a selectable locker but they require the carrier to be reshimed and the pinion depth set. Not a terribly hard job but special tools are required and patience.