I think what you have there is a 3/4 ton universal joint, which uses a short stub shaft between the transmission and torque tube, with another u-joint at the rear of the stub shaft and the torque tube. The 3-speed transmission is the same on 1/2 ton and 3/4 ton, but the u-joints are different.
You may be able to remove it from the replacement trans by sticking a socket through the center to loosen the bolt holding it to the tranny output shaft. If that doesn't work, you'll have to remove the snap rings that are visible in your third photo to disassemble the u-joint, sliding the bushings out so the rear yoke and cross can be removed. You'll need to use the u-joint that has the bolt-on bushings holding it together (like photo #4). The other one won't be usable unless you unbolt the rear axle and slide it back, but you don't want to do that, because you'll need to unbolt the rear axle to change the u-joint.
