I have a 94 silverado w 200k miles. I also have an extra 5.3l an 4L60E in my garage. I'm wanting to know how hard woud it be to install the motor and tranny in the truck and what all would I need to do it.

 

it's not a very hard swap at all. I hate to send you over there, but ls1truck has a really good write-up on this exact same swap. It's really straight forward and the hardest part is gathering all the parts together(all of which aren't hard to find at all).