It sounds like it is pretty similar to the original 110S Cosmo, but with a solid rear axle instead of the independent rear.
A saying comes to mind. "If you want to run with the big dogs...."
For what it sounds like you are wanting from the car major changes are going to be inevitable. Especially if the parts availability is getting so bad even the Australia boys can't get them.
One of the things I was trying for with my project was to use as many readily available "off the shelf" parts as I could. SA parts are getting harder to find and it will only get worse. It sounds like Cosmo parts are another order of magnitude in hard to find. Since you aren't going for original restoration, it frees up your hand to use other stuff.
The problem with finding a ball joint is that the FC uses a through bolt and clamping style of fastener for the ball joint to brake/strut lower rather than the more normal tapered and bolted set up. You would almost have to find a way to use the press fit FC ball joints with your lower A arms.
It might be possible to have a plate machined that would bolt in where your ball joints go (if they're a bolt in style) that would allow press fitting of the FC ball joint. Alternatively you could have some lower A arms made (or make them yourself) that would accept the bolt on portion of the FC ball joint.
The next question becomes whether you have the clearance for the brake rotors and dust shields with them there. Then finding out if the FC struts are the right length to allow adequate suspension movement and whether the caster would be altered with the different strut mounts on the lowers. Not insurmountable problems, but annoying nonetheless.
The rack and pinion would be the best way to go performance and parts wise, but you would be getting into difficult to undo changes to the steering shaft to hook it up and the mount for the rack has to be very solid. It could be done by building a new engine mount cross brace that would accept the rack in the right position I would think. Lots of fiddling to get it right though.
The Fox body Mustang rack that Billy used in his kit for the FBs works well for a custom Mazda application, since the frame rails are the same width between the Mustang and FB. They also have plenty of length in the tie rod arms to shorten them up a bit if needed. That and those parts will probably be relatively cheap and available for the next hundred odd years or so.
