I32 Exhaust & Islanders
FYI - My I32 has the exhaust out of the transom. I'd be tempted to place a flap on it only held down by gravity (but assure it can't flip up and lay in up position). It will likely take care of the issue and act as a check (flapper) valve on water coming up exhaust. A 90 should work fine.
There is a web site that is for islander owners. We should all signup.