I’m not sure what shortblock to put in your EJ253. I think you need to re-ask the question and provide more details. Did your engine fail and you need a new shortblock? If so just get another EJ253. I’m sure they aren’t hard to find affordably. Technically any phase 2 EJ shortblock could mate up to the 253 heads. But an EJ257 block would be a waste if you wanted to just keep the rest of the engine stock.