Making noise - driveshaft support bearing?

[midnightrider78]

The fun never stops! LOL
I have a 1972 C20 402/TH400 2wd with camper pkg and rear leaf springs.

Last week, after a couple trips hauling cars, I unhooked the trailer and noticed a rubbing/grinding noise when I drove away. It only makes the noise when the truck is in motion. There is no noticeable vibration, just the noise.
At first I thought it was the brakes but the pads and shoes all appear to have 10k or more left in them.
So, I'm crawling around underneath the truck looking for something that may be out of whack. I just happen to push on the driveshaft near the center support and it moves close to 1/2 an inch. So is that what's making the noise?

Also, if that is the problem, is there a way to know which bearing size I need before I dismantle it?(since I will be working in the driveway)