It is indeed completely different to the design of the 504! There should probably be more than two condensers to cover the whole range of neg-sizes though. If it is now set up for 35mm then the condenser position(s) and/or focal length would need changing for medium format and larger - this is shown diagrammatically on the front of the enlarger.

For multi-contrast filtration, there are large sizes of sheet-filter available from Ilford/Harman, but it would be more practical to buy their under-lens filter set. And no, it doesn't destroy the image sharpness, unless you take up growing potatoes on the filters.