You should just get it tuned, if the short block was rebuilt then just change the oil before you put it on they dyno. If the motor is built right all you need to do is get the bearing material out of the filter from the initial start-up and just a few minutes of idling. With the cams and larger injectors without the custom tune you could be flooding the cylinder was with fuel which is very bad, i have seen several people bring in cars with new motors and they drove them for 500 miles and they have a dead cylinder and the oil reeks of fuel. "Break in" is for old flat tappet cams. Typically after the install and a tune so the motor will idle we let it idle and heat cycle 2-3 times change the oil and dyno the car or truck. Let me know what the 5.4L 2v makes my buddy wants to swap one into his car, i have only seen 5.4l 4v or 3v swaps which are very impressive for an n/a setup.
