I tried searching but since 6.5 and 6.2 are both too short, it made my attempts nearly worthless.

The 6.5 in my '93 3500HD has seized up. I no longer have a need for the truck, so selling it as is means taking a BIG loss. I have access to a 6.2 for next to nothing, but need to know if it is a bolt in or a lot of work to replace the 6.5. I'm not really concerned with swapping over the turbo parts as much as getting the truck running for a quick sale.

So will the 6.2 bolt in without modifications and will it work with my 4L80E without needing a stand alone controller?

As long as you have the throttle position sensor and engine rpm/oil pump drive sensor it should work without the turbo. The trans.uses the inputs from those 2 sensors. If the 6.2 is a older 2 piece rear main seal ,it will need the flexplate for 2 piece rear seal.

So the 6.2 will use the same motor mounts and everything, I just need to transfer those 2 sensors to the 6.2 to make it work?

Yep. The accessory drive and water pump may be different on the 6.2 depending on the age of the 6.2. A 599 block 6.2 from a 91-93 truck is a drop in.