I personally believe that they are already in there. There have been several periods where absolutely no pictures have been available for many months...corresponding to tighter security measures. My personal belief it that eiother during the dry dock time or sometime just before that, engines could well have been installed.
My guess is it came from the Ukraine with at least a 90% complete propulsion plant including boilers, turbines, generators, and shafts. Most of that has to be done in early hull construction. IOW common sense would ask why would the Ukraine {Russia} build a ship to that level of hull completion to start with for themselves and not put in the propulsion plant in the early stages as needed? I don't think they would.
It's the other things that take time as well like the catapult and arresting gears etc. Then there's electronics to install galley equipment etc. Plus my guess is some internal piping may have been incomplete. The needed equipment was likely in place but still had to all be tied together welds checked etc.
The drydock period? Barnacle scraping, valve replacements, general hull maintenance, etc and adding the screws if they were not installed before purchase. But I'm betting they were there as well. If the discharge valves in pump rooms, engine rooms, etc are leaking then it's a drydock issue to repair them usually. We tried a valve repair in port on a discharge for an eductor system. We chickened out and that was likely a wise choice. We weren't sure E.O.D. had plugged the right port or not.