I own a 2002 chevrolet silverado hd with an 8.1 liter 496cid that just recently "spit" a head. Tried Napa for reman heads got one head with heavier valve springs then the other head I asked them if this would be a problem and said no through their manufacturer. Not liking the idea of that, I gave it a shot and assembled it anyway and came up with #2 problem that the intake plentum bolts were short about 1/2 inch short on one head. The casting number on both heads is 12558162 which is identical to my original heads. Question I have here is, Was there differences in spring sizes and intake bolt plentum depths? If there is, what is the year split and why? Never ran into this problem before with a chevy big block. Guess I'm a little out of date. Hopefully someone can educate me on what to tell Napa on these cylinder heads to get the right ones for the year of my truck. Thanks for any help,
Mike

 

That sounds really strange to me, but with all these new innovations in these motors I wouldn't be suprised. I don't know the answer to this so I am sending you a website called All Data. It is an online manual that covers all manufacturer specifications and technical service bulletins for your truck. It costs about $25-30 (I can't remember the exact price) for a one year subscription for one vehicle of your choice.

http://www.alldatadiy.com/