The way to know for sure is to take one rod & piston assembly and put it in all four corners and use it to measure the deck height.

My guess is that your decks are sloped a little bit. Looks like one side slops up a little bit and the other slopes down. Or it could just be random error in rod length. Depending on the brand they'll vary that much.

Probably doesn't matter much for what you're doing. Put some 0.030 Cometic gaskets on there and get it running.