That is not an OEM impeller regardless of references made by amazon…. Admittedly, I am a bit paranoid about this part only because of how important it is…. If the water pump does not work correctly, the engine will overheat and could get damaged internally. Aftermarket ignition and carburetor items are not big deal, if they fail, they will just have to be replaced, no engine damage will result. Replacing the impeller is kind of a pain also, the powerhead must be removed to disconnect the shift rod and remove the gearcase again.
But, on the other hand, you will probably know pretty quickly when you start the engine, how the water pump is working, so powerhead damage is unlikely. It is up to you…Once you get the gearcase off and the water pump removed, you will have to inspect the aluminum impeller housing and SS impeller plate for wear also…..
I found several carbs on ebay, mostly priced too high, except for this one:
https://www.ebay.com/itm/ANTIQUE-VINTAGE-Outboard-Engine-CARB-CARBURETOR-1956-OMC-5-5-HP/352940383362?hash=item522ce2dc82:g:L6MAAOSwtFteJRJu
And, it is returnable also.
We can post a classified ad here also, these carbs are fairly common…

Steve D wrote:

It would be good if the seller could take it apart and take a picture of the inside. Some of the ones I’ve seen like that often have some issues like the one you have. Can’t say for sure but that one on ebay looks like it came from a motor that was either poorly stored like on the dirt floor of a shed or barn for a long time, and fuel left in the bowl/carb, or from urine of a mouse that lived in the motor for a while. Never seen a salt water motor except for pictures, so I don’t know if it could be that either.

Steve D is correct – that carb was either laying in the dirt or it could be salt water etching. I see the listing is from Boynton Beach, Florida so it was at least exposed to salt air.

OK, well sorry to hear there was water in the gearcase. Like N2F says, resealing that gearcase probably is the hardest part of the job. It is best to pressure test first to see where the actually leaks are occurring. Pull the prop off, perhaps there is fishline behind the prop getting caught in the seal. It is also important to check the washer seals for the drain screws. There is supposed to be one and only one washer/gasket behind each of the screws…Usually, on the older engines, these washer seals are stuck in the gear housing, but it is possible for the washer/seal to come out with the screws…. So, if someone inadvertently swaps the screws, one might have two washer/seals, while the other screw has none. Instant oil leak. It is also possible that someone has added an extra washer/seal where it was not needed which can create a leak also. Sometimes, if you are lucky, the cause of a gearcase leak can be this simple. Don’t get your hopes up, but it is possible.
OK, so your powerhead appears to be in decent compression, your compression numbers were normal.
Your gearcase has water in it, pretty common for an engine this old, most likely needs a complete seal job…More on that later….
So, it seems like your next step is to remove the powerhead so the gearcase can be removed…There are seven screws that hold the powerhead onto the exhaust housing. The engine looks to be a fresh water engine, so the screws should loosen up without too much fuss. Why don’t you try loosening all the seven screws and let us know how you make out….Don’t force them if they are stuck, you may have to use heat. Make sure you use a decent larger screwdriver that fits into the screw heads nicely…
If you get the powerhead off easily, go ahead and disconnect the shift rod from the shift handle, remove the four gearcase bolts, then remove the gearcase…
I would put an add in the wanted section of our classifieds here, someone will have a decent carb for you….D
I know that Ben Dittmar has a nice youtube video on servicing one of these engines, including resealing the gearcase…