I am by no means a 3D expert, but we have been fairly happy with Autodesks relatively new product called Inventor. It has good 3 D support (much better then plain Autocad IMO). It hass sheet metal design built in and can use canned fasteners, etc. It is not cheap, and is now bundled with Inventor, Autocad and Mechanical Desktop (runs on top of Autocad). It looks like the major drawback to inventor is its lack of good support for doing complex 3D contours (like the GT40 body). They would have to be done in Mechanical Desktop and imported. Otherwise Inventor is a fairly slick and new way of doing 3D, etc.