A couple of reviews from a few years back said their individual products had some fit-n-finish issues, like some seemed to mate right up and some seemed to have been welded/constructed while drunk, but with any header and mid-pipe changeout, the biggest issue is getting the M10x50mm bolts and new OEM ford gaskets for the header-to-midpipe connections to avoid gasket blow-by...
do a thorough search through old threads here, and you will find posts about it from me and others who have gone before you... good luck!
(BTW, just my opinion, but headers are a waste of money and time if you are not going to cross the 500HP mark anytime soon... better to spend on good midpipe and mufflers and then spend the rest of the money you would have invested in the header install into other mods... just my.02... )
shaun