here is a good info page regarding the heads:

http://www.sallee-chevrolet.com/Cyli...ads/Vortec.cfm

down towards the bottom of the page, they list some plugs
including Rapidfire #3 (an AC Delco plug)

From the plug length info on this page, you can do a heat
range comparison on your favorite plug brand's web page.

mike in tucson