Ughh Serial number and head numbers

[Cattz]

Hey guys.
Im kinda stumped, and now asking the experts.

Basically, Im looking, (found maybe), a cylinder head for a 1984 Merc 150 V6.
The serial number, 6181505, shows up in some places, and non-existent at others. Are my findings correct for that number?

The head number that I have is, 18419-C2
I found a head, that looks the same, but that number is 18419-C
Is there that much of a difference? What is the C designation?

Cattz

[boats.net]

Unfortunately you may need to contact Mercury direct for the information. I do not have access to casting numbers or specific dimensions.