OK I'll ask, Merc's website shows the part numbers I list above, where did yours come from and why is Merc on site in error?
Bravo402's serial number starts with 0M, the serial numbers shown above are for the 0W and above, his engine model would need the 0W and below.
Also in post #8, he mentions his is standard cooling which coincides with looking up his serial number as standard cooling and not closed cooling that could have been added later. If he didn't mention standard cooling, we would have had to ask him if he had standard or closed cooling to confirm the correct part number.
First run the serial number to confirm their engine model and parts catalog part number, then go to the website I linked above for both the most latest part numbers and the original part numbers. The Merc website were you punch in the serial number only shows the original parts numbers, it does not show or keep up with the superseded numbers. You'd have to pull them numbers and run them in another area to get the latest numbers or go directly to the other site after confirming what the OP really has.
The best place I have found on the internet that keeps up with the latest parts info as Mercruiser changes them near daily it seems is here.
http://www.mercruiserparts.com/partsByNumber.asp