I was talking to a guy regarding two 258 short blocks for a rebuild doner and on top of the pistons is the number 58 stamped into them on both blocks.

Would this be a .60 over bore or could this be a stock marking?

I thought it unusual for two blocks to have the same stamp on the pistons. One of the blocks is an 84 and one is an 85. He said the current one in the jeep (85) has been driven not much in the last 10 years since he had it. If true that would make it going from stock to 60 over bore within 10 years. Possible but seems a little extreme doesn't it?

Thanks in advance for any help,