Found this company that sells a swap in/bolt in 273 and there's quite a big difference between the 2. looks like some things need to be relocated.
http://shopspeedhouse.com/duramax-t...rub-fix-nv273-conversion-sas-kit-upgrade.html
"The ABS brake module on the driver side frame rail will need to be re-located rearward approximately 12 inches due to the sheer size of the NV273
Use five pieces of 5/16"x12" inverted flare brake lines from most any auto parts store (roughly $20)
Use five 5/16" female x female inverted flare couplings from most any auto parts store (roughly $10)
You will need to power bleed the brakes, or have it done, after moving the module
You will re-use your original shift motor - be sure to remove it from your NV263XHD core before you send it back!
Depending on the cab / bed combination you may need to extend the transfer case sensor harness / shift motor harness 4 to 8 inches"