I searched and didn't see a thread that fit, so at least I tried. I think Pete McCarthy's book on Pontiac parts numbers is the best and I have many (but not all). For some reason eBay and Amazon think this book is worth $100, but you can get it from his site for $35.
Back in the late 80's and early 90's I would take this book with me to the junkyards in CA to look up stuff I'd find. I had a 69 Firebird 400 4-speed car with a numbers matching engine and #62 heads, so I wrote him a letter (that's what you did before the internet) and he responded. He said he's seen this before, but though it should have had #48's it's not something someone else did, but it was a factory thing, which makes sense because #62 and #48 are for all intent and purposes the same head.
I'll enclose a link because this book is a wealth of knowledge for block/head/carb/intake/exhaust numbers etc.
What are your favorite books that you have no affiliation with?
http://www.petemccarthybooks.com/ind..._1955-1979/196