The TAC is the Throttle Actuator Control module, it is what controls the DBW throttle body. VATS is Vehicle Anti-Theft System, it will need to be programmed out for the engine to start.
2004 will be a DBW engine if it came out of a truck, but vans were mostly DBC until 2007 or so.
You can buy parts like radiator and engine mounts without having the engine, but when buying an engine, if its DBW, be sure to get all the electronic parts, TAC, gas pedal PCM, etc. all from the same vehicle to avoid mismatch issues.
Here's a link to my green truck I did back in 2012. The prices are probably a little out of date, but will give you an idea on what all is involved.
https://ls1tech.com/forums/conversio...71-c-10-a.html I do things in a somewhat unconventional way sometimes, so take that as you may.
