I think it was the position of the bolt holes in the bow. These look like the correct ones because the bolt holes are horizontal not vertical. And have the stop knocks.
These bows look to have the smaller, rectangular holes for the 1/4" oval necked carriage bolts used on the trailers. The M37 bows should have the larger, square holes for 5/16" square neck carriage bolts, if I remember correctly.
“When a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, IT IS THEIR RIGHT, IT IS THEIR DUTY, TO THROW OFF SUCH GOVERNMENT...” -Declaration of Independence, 1776