U Joint Replacement Questions?

[YourBuddy'sTruck]

Hey Everyone.

I've a '70 C20 with a 350 and a 350TH Auto tranny.
The rear end is a 14 Bolt, and I'm not sure if it's original or not.
That leads to my question about he U Joints.

First, would they be some form of Conversion U Joint?
What is the likeliness that I'll be able to change them in 2-4 hours time?
Is it easier/faster to pull the whole shaft and do it on a bench?
Any advance advice would be greatly appreciated!

I haven't changed U Joints since I was 16yrs old and it's been a bumpy 26 years since then. I recall it being easy, but worry about getting it done in time to head to work?
Here's a pic of what I have. And the one with the clip is "clunking" and on its way out.