@ the original post, I don't think anyone has swapped engines in a NBS,
its plausible, the biggest hold back will be programming ( read access to a programmer)
The main components, engine, tranny, ECM and BCM will need to be swapped out and reprogrammed to work with all current options you have for them to work.
Are there cheaper more practical ways to get the torque you need.. probably, but its a do-able project..(money no object)

I think ousig2408 is right about the gearing and turning being the common man approach and sub $1K for sure...

 

it would be a lot easier/faster to find a Yukon w/the 6.2 or the rare 09 tahoe w/the 6.2 or an Esky....

 

Or Denali.

Probably the next most practical way would be a Procharger for about $7K. But you can definitely kiss your power-train warranty good-bye.

 

im running a STS turbo on my 5.3 07 an let me tell u somthing i get ghost 0-60 5.0 1/4 13.4