in the tune you take a degree of timing out at wot. the high compression block dont like as much timing when boosted or you get KR and thats what chips pistons. top swapped you dont want any kr. along with a bunch of other little things changed to make the tune better.
a bottom swapped engine with the stock pulley runs about as fast as a 3.4 pulley on a l67. so its gonna have a bit more power vs what your used to.
not many can do a caned tune for a 05. over kill is about it iirc you can buy a dhp interface for like 250, and tune it yourself, or ive helped a load of guys out via email. only you need to have a dhp tuner on your end for that to work.