not positive it has a torque tube but every stock 1/2 ton AD truck I have seen has one. the driveshaft is inside a tube directly connected to the rear axle on one end and through a single ujoint and sealing spherical ball connection bolted to the rear of the trans at the other end. the rear axle is not bolted to the springs with u bolts like newer trucks but instead the axle housing bracket where it connects to the springs has a pivot bolt to allow the angle of the axle, relative to the springs, to change as the suspension travels up and down. the driveshaft can be unbolted with the spherical ball end at the trans and taken apart at the rear axle end. the inner shaft is splined and connected at the pinion end with a cross pin which can be removed for complete disassembly if required. there is a shaft bearing inside the tube, called an okie bushing, that can be serviced/replaced. if you decide to swap out the engine and trans to something newer without the torque tube there is an aftermarket axle bracket available to mount a different axle on the rear springs. the bracket basically locates the axle with the locating pin offset so the axle is centered on the springs.
here is a link to the rear axle torque tube.
http://chevy.oldcarmanualproject.com.../5212mts00.htm