Short of the fact that the machines already exist, there is little to recommend burning oil in a steam engine, rather than in a diesel. If the fuel is suitable for diesel combustion, then the efficiency difference will be immediately apparent.
There is rather less need for a fireman in the crew, though, as fuel transfer can be more easily automated.
IÉ oil-burners were identified by large white discs on the smoke-box door and the sides of the tenders.