Difference between Mercury 225 heads

[pmcs]

Hi Folks,

I have a 2000 Mercury 225 EFI (S/N: OT076229) and am replacing the port head.
The one I removed has a casting number of 812851-C11. Manual shows that I require
P/N: 812851A16. Everyone is telling me that the casting number doesn't matter and that I can even use
P/N: 812851A 2, which is for a different serial number of my model.

Can someone tell me the differences between the various 812851 castings and part numbers ?

Thank You,

Eric

[boats.net]

According to your serial number you require the 812851A16. I do not have access to specific information on castings or dimensions.

[pmcs]

They seem to be identical and work fine.

I suspect that they may have different volumes (in cc's)
but other forums are saying that the head volumes can vary
up to 150 cc's between heads with the same casting numbers.