Anything can be done, but this would not be easy at all. You would need at a minimum an 03/04 chassis harness, ecm, nsbu, address the fuel gage, vats re-learn and everything that attaches to the lb7.
Like what James says above, can you not just use the top end off the lly and put it all on the lb7 then you'd have a complete running lly again (with an 01 short block). This isnt so bad, essentially just a head gasket job and turbo.