706 Castech heads?
 

I found a 2003 Silverado for sale at a dealer, with 73K miles. I'm interested in it; however, it has the number 706 cast into the passenger side cylinder head. I've read about the Castech cracked head issue with these.

So, I have some questions. 1) Are all 706 heads made by Castech? 2) Do all of the Castech heads develop this problem or only a few? 3) How difficult is it to remove a valve cover to look at the head? I thought about having a tech at the dealer remove a valve cover to look for the Castech logo on the head before I make a decision about buying the truck.

Thanks in advance for any advice. The truck is reasonably priced. It would replace my rusty '95 C1500 Silverado, which needs at least $2500 in repairs...I wouldn't want to go from that to something even more expensive to fix!