A complete GTR cradle compared to a GTS or GTS-T would be similar in weight but provide a lot more strengh to handle the extra two cylinders.
We did the conversion to alloy GTR hubs on Clinton's R32 and saved 3 kg per hub (the important part though is the reduced unsprung weight).
Heavier parts include the shafts, diff housing and additional front diff support bracket.
Common parts are the top arms, traction arms and lower arms (the only difference on lower arms is the balljoints).