Interesting discovery inside 318

Upon disassembling the 1984 318 for my son Jason's project car, we discovered something very interesting. Just wondering if anybody has ever run into this.

As you can see from the pictures, 7 of the pistons are flat tops and 1 is a 4 valve relief piston.

The engine has been together for years, and appears to be mostly factory.

I know Chrysler quality control in the 80's was lax, but was it this lax? Dealer replacement piston? after market hack job.

Thanks. Eric and Jason.