To do the swap you'll need a new water neck, new upper rad hose, Mallory FPR (pn 4309), and everything Bonzo said. My tach is also off after the PO carb swapped my IROC, but that could just be because he's an idiot.
My opinion:
Comp XE cam, Vortec heads, RPM Performer intake, Holley 650-750.
VERY proven combo with drivability dependent on cam size. All should swap over to a 400.
http://www.thirdgen.org/techboard/af...ad-xe-cam.html