design
I don't think it's totally a design problem. If the inside of the engine module had bulkheads against the port and starboard walls, then there would be something to push against when mounting the shoulders. Another possibility would be to make the lower shoulder out of two parts vs. one. (in other words, the first part would be the long box shape that is actually mounted against the engine module, and the second part would attach to the lower side of the block...if that makes any sense at all....