A CARB number is a California thing. It makes your parts legal and considered to be stock replacement parts in the state of California. It stands for California Air Research Board. My heads are one off. To get the proper pushrod length you use a push rod checker, you can buy a set up complete with instructions from Summit racing. I don't actually use one I use a very old tool setup that I have had for over 45 years. Dial indicator, light spring and a brain basically.