Have a line on a 2004 5.7L Hemi, Is this a good swap candidate?

Did he give you the mileage?

Do a leakdown test. If it passes, buy. Then swap valve springs and run it.

Your list looks good. Couple things:
-Milodon 31000 with correct pickup. Can use factory truck gasket/windage IF you put RTV in the right places. Otherwise you also need the milodon windage and gaskets.
-For fuel system - also need a wix 33737 corvette regulator/filter and all fittings
-Electric fan - don't need a switch- can be run by megasquirt (through relay).
-Headers - will TTI's not fit? Do you have power steering or manual?
-Brackets - will TTI's not fit?