I agree with Driven5, that the Deltawing car is a good example of how pretty extreme rear weight bias, similar to what you can have with a rear engine layout, can work. Yes, the moment of inertia will be lower for a rear-mid design like the Deltawing, but it's still a lot of rear weight bias.
There are other advantages with a rear engine, such as the possibility of easier engine removal and replacement, with only a floor jack instead of a cherry picker/hoist. The shifter will also be much easier to make "Miata-like" than a typical rear-mid design with their complicated linkages or friction adding push-pull cable shifters. The bigger rear tires (and smaller fronts) you will be driven to will look good.
To go along with the "Not too short" wheelbase you may want with a Corvair engine in the rear, you could recline the driving position more than normal, lowering the CG and making the car look cool (yes, here come the "too low for the street arguments... Noted, but that's no fun. Just drive like no-one can see you, as much as possible, and maybe mount a wing to the top of a full roll cage to act as a sun shade and "see me" device). One or two wedge-shaped gas tank(s) between the seats and engine compartment, on one or both sides of the transaxle, will put the tank close the CG location. A battery way up front may make sense, but closer to the CG is good for a gas tank.
Regarding the suspension system you mentioned, how will opposing the normal tilting of the chassis while cornering, braking and accelerating, or even tilting the chassis opposite the normal roll or pitch angle, improve grip? I think simpler is better.
Your plans sound great so far. I'll be looking forward to seeing what you come up with. I'm curious to see where you run the axle tube of the DeDion rear suspension. Will it be above the transaxle, or will there be room to run it below? Maybe a frame of light members that are both above and below the transaxle like a Lotus 58?
Attachment:
Lotus 58 DeDion Rear 1.jpg
Attachment:
Lotus 58 DeDion Rear 2.jpg
Dean