Without a doubt run the CAS. Tony is the only one that actually designs these and has the tooling for the newest in core technology, extruded tube and fin. Cottons piece might be big, but CAS has 3 front mount sizes and Cottons cores are spearco, or bar and plate. That core has been passed twice due to newer technology. 1) tube and fin 2) extruded tube and fin.
My V2 fit fine with the sway bar, and Cottons piece is designed after CAS so they bolt up and fit the same. They are also priced very close to each other. CAS is the only vendor with flow numbers from a flow tunnel though. CONFIDENCE comes to mind on this issue also.