I own a pr. of new Cummins 370 RECONS. Just turned 520 hrs. I do not know much about the JDs. I'm a fan and proponent of the Cummins 6BTAs. I know their strengths and weaknesses. Superb engine, 1,000s of 6Bs out there, parts are cheap, easy to fix and the Cummins 5.9 is as reliable as a diesel gets. Setting the 6BTA up or any other diesel is ALL about not overpropping the engine and exhaust design. After that routine maintenence. Best I can do for ya. BTW, the 33 YB is a very nice hull ! Get on to www.sbmar.com. All you need to know about marine diesels and Cummins 6Bs is ALL there.