you are right and wrong on your metals. the 2001 wheels were made my alcoa and are forged. the 2002-2004 were made by speedline and are a spun cast, that makes them stonger and lighter than the forged 2001's. they look the same, the speedline wheels have there name cast into the back of them. they cut 1/2lbs per wheel by going with them.
c5 to c5z is huge, not only is the weight less but they went crazy doing it. the windshield is 5lbs lighter but just as hard, the suspension is way different(shocks, sways, springs, alignment) the LS6 is in it and the M12 transmission, it has different gear ratios than the MM6. Fixed roof on the vert frame. no fog lights, it got brake ducts. manual power seat with a 6 way power driver. the cluster says Z06 on it. Ti exhaust from the axle back.
there is more so you can read up on it here.
http://forums.corvetteforum.com/showpost.php?p=1551356372&postcount=4
i wouldn't waste money on a non C5Z, even with upgrades you would have the same money in it than if your "buddy" just bought a Z. if "he" wants to ride in mine or look it over just PM me.