To create pronounced ribs for Genesis 3 Figures you would be looking at either applying Normal maps or using Geometry Morphs.

There are numerous existing Body morph sets for the Genesis Figure range which can be used across the entire figure range using utilities such as Generation X 2 from Dimension Theory at Daz 3D.

Its hard to say which ones would suite your specific requirements based on your description here. But maybe a Character preset for Genesis 3 Male such as Giani 7, or even Lee 7(HD) if your looking for something slimmer, would be the simplest solution. Character presets can be used either as a complete morph including the head or just as a body morph.