Last time I spoke with them, they were using a straight off the line LMM VAN engine, adding their own water cooled exhaust, charge cooler. and some small parts. The reset of those pieces are Mercruiser. They ran a custom tuned LMM ECM (360 - 500hp at crankshaft), paint it white, and slap a $35k sticker on it. Not bad, when the US Gov or NATO is your intended customer.
For the marine tuning side, I've got that part down pat. Saved 20 some revisions files over 4yrs, on top of the purchased DSP5 LLY starter tune. Lot of tweaks like torque limiting to protect the outdrive, major idle related changes, and drive ability remapping cause boats never coast. 300 plus trouble free engine hours later, I'd call it bullet proof. Don't know any floating Duramax platforms even close to that number yet.
It's not hard to bolt one up in a boat. Making it run strong, and last like you'd expect a diesel is where I evaporated 30k in a year. lol... But the LMM is a great starting point now, vs the LLY at least. And I feel it's the go to platform if we can make an affordable swap package. There is other changes required like drive gearing and new props that might cost ya as much as the engine swap.
I owe a big shout out to guys like Fingers who helped explain the weak points, and Curtis who blew up many motors to prove ya can't spin one 5000R's in a boat all day. Lot of comments were taken to heart, so gotta give credit where due. Reason I always try to help out the next guy who wants to tackle a crazy swap.