With the complexity of the electronics there are several companies who specialize in takeout packages like those described, often with a good warranty. Pacific is one, located out west - Take Out Engine Packages - Engine Packages - Engines - Engine & Transmission - Products

Also some offer new equipment in a complete package -
Chevrolet Performance LS Engine & Trans Packages

Just remember, "Let the buyer beware", especially applicable when buying from an individual, with no warranty provision.