help identifying Mercury powerhead

[hallett19]

I got what I think is a 2.0 150 Merc powerhead. I just want to actually verify it. Found a number up on top of the block on a round piece, looks like a freeze plug. B315092 is stamped on it.

Can anyone tell me what this is.

[hallett19]

I also found this set of number on the block just behind the trigger arm near the #2 cylinder. the number is 011888 2

[mach351]

That second number is the build date - Jan 18,1988