I had a valve seat come loose and it damaged the head to the point that it is not repairable. I need to replace the head which are very hard to find. The part number listed for this head is 831656 and so far I haven't been able to find one that I have any confidence in buying. I understand that the same head is used on the B 18 or the B-20 automobile engines but I'm not sure which one is a direct fit or if there are any modifications necessary to adapt them to the marine block. Does anyone on the forum have any experience or knowledge in doing this part swap?