Upgrading DDE 4000 HP to Unlimited DDE,

I am employed in the Yachting industry but unfortunately I am USCG licensed, and most all engineering
Jobs are limited to MCA license credentials. I am attempting to get upgraded to a license that will get
me a MCA equivalency of Y4 or Y3. I hope to get upgraded to the Chief Limited (1600/3000 ton) Near Coastal and the 4000 HP DDE unlimited. Does anyone have any experience on the possibility of getting
an MCA equivalency while holding these USCG licenses? Concerning the HP designation of vessels, if
I am working on a vessel with (2) 2650 HP diesel engines, is this time considered as engineer of a 2650
HP vessel or (2x 2650) a 5300 HP vessel? Also, as the USCG requires time as “supervisory position” does time served as the only engineer on a vessel (such as a yacht or a gambling boat) qualify as supervisory position?

Thanks for the Input