Make sure you have the rods oriented correctly on the crank. (chamfer side of rod to cheek of crank) You wouldn't be the first person to make that mistake if indeed that's the only problem. If you reverse them they won't fit. What are the measurements of the rods?
I both sell and use the Molnar cranks and rods and have never had an issue with anything I've gotten from him.

machine shop owner and engine builder