yep I have them both,

both hulls are ABS, The Neptun has a wooden deck, no motor mount, however adding a block of limewood or balsa, epoxied into the base of the hull it can accept a motor mount of your choice,

I run mine on a vison 400 type motor. fittings kit is seperate though, however if you want, you can quite easily put on a new super structure. I have seen the Neptun done "cab-forward" with the super structure on the front hatch, with a centre island grafted onto it and a sub on the back on an A-frame, also "cab centre" as on the box, and "cab-aft" like most modern cargo ships, and thats how mine runs. its almost HO scale judging by the railings that come with it, so detailing it wont be hard, just call you your train shop.

can be made to run on a 7.2v ni-cad type pack with 1.2 kg (2.4lb) ballast
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Sydney Star is essentially a BIGGER version, rather than a coaster, its a long distance trans-pacific panamax boat, propshaft mount doubles as the motor mount. needs bow and stern thrusters, however if you dont want to buy them, you can plate over the pre-drilled ports with styrene, then fill the exterior to smooth out the profile.

battery recomendations ate 2x 6v batteries, however I run 1x 6v battery with compensating ballast to settle her, 3x speed controllers and a 4ch rx.
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in both cases use Robbe rudder 45x40mm on a 70mm shaft, I think its part 1481.

pictured below are 2 shots of My neptun "GEMINI" sailing in choppy water, thanks to full size speedboats, and my sydney star "Celestia" with her crane (now removed), sailing in calmer waters.