Other than removing the vacuum advance and venting the distributor body, what else would be required to marinize a GM HEI distributor?

I bought one from DUI years ago and loved it for it's simplicity and reliability. I don't want to spend the $300 per engine when I can buy a new HEI for about $130.

Any thoughts?

I have successfully removed points distributors from boats for years and used the Delco HEI. People love them. Mostly I have done Crusader 454s in inboards, never in a high performance application. I adjust the advance curve with lighter springs and do not use the vacuum advance.
Hard to improve on the Merc Thunderbolt IV.

Thanks Ed, I've got Merc ignitions now and have had several modules fail over the years which is why I want to make the conversion. Plus, the HEI really simplifies the wiring which, on a 29 year old boat really could stand to be simplified.