check over here:
http://www.hobbytalk.com/bbs1/forumdisplay.php?f=21
bud and those guys can help a lot with your sc-18.
from my experience on carpet:
kit red springs
orange fronts
blue rears
high flex t-plate
that will pretty much be the basic of carpet set-ups, but it will work. they're designed to run excellent on carpet right out of the box, with the exception of the optional ball diff, there's not much else you need to do to it.
for oval you might want to look into bud's lto chassis