I'm starting to get a little worried...

[82 GT]

In a previous post of mine, I mentioned the fact that I heard some squeaking and clicking noises during acceleration(and vibrations). I was advised that it's most likely bad U-joints.
I crawled under the car and held the yoke with one hand and tried to jiggle the shaft with the other and got a little bit of play in the joint. I'm scheduled to have the joint installed tomorrow but I'm starting to wonder if that's actually the problem.
When I let out the clutch in reverse, I usually hear a loud "clank" or even when I let out on the clutch sometimes I hear the same "clank" sound.
I'm just hoping it not coming from inside the tranny.
Another thing that makes me wonder is if I'm cruising in second gear and I quick punch the gas a couple times, I don't hear a "click-clack" sound as you would if there was excessive slack in the joint.
What do you guys think? Like I said, there was some play in the joint when I checked it but after I did that little test in 2nd gear, I started to wonder.