Chevy Small Block Parts... 67-68 change?

[toms68cst]

Why is it when you see Chevy small block parts (Like rebuild kits) advertised on ebay or somewhere else do all the years range ..... - 67 and 68 - .......? It always seems like there is always a break between 67 and 68. Were there any major changes were made to the small block between 67-68?

I'm thinking of the 327/350 which of course was available through those years. There always seems to be a break at the 67-68 years.

The only thing that comes to my mind is the introduction of smog controls in 68. If thats the case how would other engine parts change?