I know that sounds a little open ended, but let me explain:

I have to create a mounting bracket to hold two different units (one is a pump and one is a hydraulic cooler). The pump was downloaded as a step file, so I have a shape for it - but it doesn't have any material assigned to it. The hydraulic cooler is an assembly with a million (exaggerated some) parts in it..which would really slow down my computer to bring it in as an assembly.

I want to be able to draw a rectangle to represent the size of the cooler and then add my own weight to it. Then add weight to the pump and place them on the bracket so that I can find the balance point of the bracket (side to side). The purpose is to create a single pick point that would allow for a vertical without horizontal wobble.