At this point, I've designed the entire car in 3d but with only an approximated suspension. Suspensions are notoriously difficult to design, so I'm waiting on a set of plans based around the Mustang II double wishbone suspension, which is the go-to suspension for street rods. I've even seen it used in VW type 1 and type 2 bolt-on kits. It's a proven design and aftermarket parts are readily available.
I'll build the cross members to spec using box beams and then attach all the metal parts in the correct locations. This way, front and rear suspensions are modules that can be attached to the box beam frame member. That said, I will probably extend the suspension side walls longitudinally to form a longer bond surface to the frame.