Here's a bunch of questions for you.
Is the EJ257 block new or used?
Have you matched "bored" the cylinders to match the pistons, or did you just drop in the pistons?
Did you check the piston to cylinder wall clearances?
Did you check clearances before assembling? (Plastigage the bearing mating areas when torqued down to spec)
Sorry for all the questions, just want to understand your build. Maybe more questions to follow depending on the answers.