251, and 253 are phase 2 engines (25D phase 1). The parts for these engines should be interchangable. If you have found one, you should have the specs for the other. I will look through my "pile" and see what I find. JE should know better than build a "bad" piston. Then actually SEND it to a customer is ridiculas.
Do you know the actual specs of the pistons (measured them and compare to what you ordered)? are they 8:1 and the rods just don't fit, or are all the specs just screwed up compared to what you ordered? Maybe you got a set of pistons from an apprentice.
Did they tell you when you ordered them that the ratio you wanted would be hard to do? If they didn't, send them back. They sent you trash, not what should be expected from JE. If they did, they still should not have sent them, but it would be nice if you can blame them ENTIRELY, and not have any directed back.
I think that the factory service manuals should have that info as well. I have the engine section for the EZ30, and I am thinking that I have seen the piston specs in there somewhere.