guyan reduction

Guys, i want to experiment a little with guyan reduction in a dynamic calculation. So far, I never found the need for it but as models are getting bigger and bigger I want to see if it is advantageous to use without losing accuracy or results.

I have a model of a ship, and i want to do both a natural frequency analysis as well as a forced vibration analysis.
Am i correct in understanding that I need to put the stiff elements (longitudinal and transverse girders,beams and other stiffeners) in the A-set and leave out free platings of decks, walls and ceilings? Will translations in those plate fields still mean anything? Or do i need to "activate" any point i want to check for the response (meaning including such points in the A-set?

Thanks in advance.