Technical 4bolt-main-different-n-the-odd

Yes. $$$

 

.....net pic

 

And, they don't have 4 bolt mains, those 1962-1967 chevy ll blocks.

 

Yes.
1965 model year and early 1966 used the "721" casting, the common block for the major part of 1966 was the "362" block casting as well as 1967.
There were Nova "service replacement" blocks also but I have never seen one personally.

 

Here are my two "High Nickel" blocks.
I had already bought the first with a load of spares I didn't want and the chap that came to have them said OMG do you know what you have, bla bla bla they are hard to find.
I guess from the P/N on the rear that could have denoted a different production run with a different metal mix.

One thing I have noticed with them is DAMM are they heavy, I have had Pontiac motors before and I would say I haven't noticed these being any lighter, maybe even a bit heavier. I can't move a block on my own, I had to get a friend to help get it out the back of my car.