Mercruiser exhaust

[dingman29]

Forgive my ignorance. I have very little knowledge when it comes to marine applications.

I have an 86 21br with a 5.7 carb engine (mcm260). I am fighting what I believe is water reversion. Engine had an exhaust diverter system added to it (imco sound advantage).

I am working on making the boat stock again as the system doesn’t work and seals are gone. I could run the boat at a higher rpm and no water would end up in the motor, but left to idle for about 10 mins, and there would be a bunch of water in the oil pan).

From what I’ve gathered, exhaust elbows are part #s 11086t and 14343t. The y pipe I have is round. What is the difference between port and starboard elbows?

I found that 14343t is a round opening at the by pipe. 11086t seems to have an oval opening when I search used or new. It seems odd that the exhaust would go from oval to round on one side. I am trying to get some clarification. In the parts diagram I pull up they appear to both be round, but it’s also a sketch and not an actual photo.

Serial number does have the 1st digit rubbed off but it appears to be B-424336 (not sure about the first “4”).

Any help would be greatly appreciated.