I don't know anything about Olds engines, but SBC block numbers and casting codes can tell you if it has a high nickel block.
An 010 or 020 cast number under the timing cover with tell you it has high nickel content. Also the last three digits 010 at the end of a rear block number tells you the same.
Get the block casting numbers and Google it up to see if any other racers out there have the block code number references for you to check... that is if he doesn't lie to you and give the numbers he wants you to believe they are...?