dd 2 cycle otherwise known as 4-53, 6-71, 8v-71, 6v-i92, 12-71 and many other iterations is a pre wwii design engine that was extraordinary successful and is still supported today.
The dd 8.2 is a 4 cycle engine introduced in 1979. Approximately 200,000 were made before production ceased in the very early 90’s. It is widely believed that only 100,000 engines were put into operations and the second 100,000 engines were used as warranty replacements.
If i had these engines in my current boat i would just keep on enjoying them. However, if i was shopping for a boat i would not be willing to take on the liability that comes with maintaining a 35 year old engine with next to no aftermarket support. I have the same feelings about the cummins 555.
I would have no issue taking on a 50 year old dd 6-71 as there is tremendous aftermarket support for that engine.