The timing of a turbo cam is a little different from a cam for a normally aspirated car, but the same general rules hold true. Longer duration is good for high rpm, and will cut down on low end torque. A lot of overlap will hurt idle, even more than on a non-turbo car, but can help at high rpm. Since the Buick is not really a high rpm engine, the range of cams that can be used is not as wide, so that limits choices some. And do you want to go with a roller cam, to minimize the possibility of a wiped cam lobe? Most of the vendors will help you make a choice- Full Throttle, Jack Cotton, Weber Racing, etc. And they will have all the parts you need to make the installation. So decide what you want, and talk to the vendors.