OK so after much discussion, debate, desk slamming, and paper crunching yesterday, I was able to connect with Autodesk technical ace Ken Fauver. Ken informed me that although you cannot get the equipment dimension data strait from Plant 3D, you can get it from the manually entered data on the corresponding P&ID. My issue is that I don't have any P&ID's on this job, just the model.
I would love for this to be a feature in upcoming releases of Plant 3D. If nothing else, just the bounding box info of the object would be fine. I can get some of the data I need through arx but it's a hassle. Would be nice if it was already there .