I am just on Mace's website and looking at the CROW VX-VY V6 Ecotec Cam and MACE Computer Package. In terms of fitting, how long would it take to replace the camshaft?Would I need to change anything else on the engine?

Replacing the camshaft approximately requires a day by someone who has mechanical experience and knowledge in regards to engine building. Therefore if you do not posses these skills, an experienced mechanic would be able to do the work. This particular family of cams is designed to work with the stock valve train.