First of all, what is the L32R crate motor? I can't seem to find any info on it. Unless they've changed the name of it in the last 6 months, I don't see it anywhere. I'm curious about the specs.
Secondly, a 5.3 is an LS motor. It's in the same family as the 4.8, 5.7, 6.0, etc.
How quickly it can be done, depends on one thing . . . MONEY. If you have a lot of it, it can be done in no time. There's probably a shop that would do the swap for you, and alleviate all of your worries. If you have a lot of money, and rush through the process, then it will also cost you more in the long run.
For a home mechanic, yes . . . it is a lot of work in a short amount of time. Epecially so, when you've never done a motor swap. Before you even spend a penny on motor or any other part of the swap, you need to research the process as much as you can. Use this forum, Performance Trucks.net, and google message forums for 1988-19988 Chevrolet/GMC/GMT-400, etc. There is tons of info out there. Research the exact parts you will need for your own particular swap, and where to buy them.
These are just a few of the general things you will need:
*LSX engine - your choice.
*Transmission - I suggest a nicely built 4L60E (if you must), but prefferably a 4L80E
*PCM - 0411 PCM is preferred
*Engine harnes - you can either buy a custom harness, or re-wire the harness yourself. The first option is expensive, but the second option will drive you insane.
*Custom tune
If you take your time, you can do this wisely, and save a lot of money. Or you can rush it, over-spend, and make mistakes. The most important thing is RESEARCH. I hope you take your time, and make sure everything is done correctly.