When trying to do front end alignment- How many inches from back rim to front rim on 92 silverado Chevrolet pickup?

This is called wheel base and varies from model to model.

In an alignment measuring this with a tape measure will just mess you up.

The rear wheels need to be straight ahead in relation to the frame of the vehicle to prevent dog tracking (technically thrust angle). With a tape measure you would pick a perfectly centered point near the front and measure to the axle on each side to see if it was sitting square under the truck. This is not realistically possible. Computerized alignment machines do this somehow if you check the rear wheel alignment.

But strangely the front wheels do not need to be exactly side by side to work correctly. This makes checking the wheelbase useless.