not neccasarily their fit up in question, but the quality/strength of parts. many pieces tend to bend, but as above i did post a list of a general consensus of parts that hold up and those that dont.
there are some parts that are ok through integy, but definitely a long list of no-good.
i usually utilize this list:
http://www.beatyourtruck.com/forum/showthread.php?58258-Integy-what-and-what-Not-to-buy&highlight=integy%20buy
if possible in all cases though i try to not get their aluminum...