340 questions - anybody recognize these pistons?

I started pulling the 340 apart that came in my 70 duster project. It's 0.030 over with these pistons in it............casting date 6-72. Has 1970 X heads on it. Appears someone polished the rods? What advantage would this serve? Are these stock rods? It did also have a windage tray in it.

Block info: Cast date: 6-7-1972, part number 2780930-340-2. Passenger side has 3B137371 stamped into it.

K Member: I'm thinking this a newer K frame based on the motor mounts. Do these take a motor mount more like a 70's and 80's truck would?

Just trying to figure out what I am starting with. Your help is greatly appreciated.

Thanks! Pauly