Your post is unclear. You are using a '01 block and are swapping the heads and valves over? So I take it you are going to run the 2.5L heads with the 3L valves in them right?
IMHO that is a great combination and the heads should bolt right up to the 3L block. Make sure to prep the heads a little bit. Above all, read through the old posts in this forum as I did almost the same route, but I am too tired to rewrite everything again. You should find what you are looking for with the search routine. Most of us have detailed all the important points in these previous threads. IF after reading all that it isn't clear, then as us some questions and you will find MANY helpful answers are out there.
Good luck.
warmonger
