It's known as a 4 speed crash box because there are no syncros. Shifting involves double clutching to bring the main shaft to the speed of the flywheel. It takes a certain feel to get it right.
If you have a 3/4 ton, then you have an open rear end. You could swap that 4 speed out to virtually any other transmission with the right adapter plate. However you would have to figure something out for the parking brake.
