Those double sway bars: damn they wanted the thing to push, didn't they? FWIW: the best handling AX Spitfires I've seen have massively stiff front springs and minimal sway bars, making the car corner very 'flat'. Probably not a real good idea for road racing, though. The front springs look a bit spindly.
Hard to tell for sure from the pictures but it looks to me like the steering rack may have been moved back. Stock Spitfires have the rack too far forward making for some really weird Ackerman. On the stock setup, if viewed from above the tie rods sweep back, when they really should be either straight or sweep slightly forward. Problem is, when in the best location the rack occupies roughly the same spot as the #1 connecting rod journal and the rod journal wins that fight. Unless the engine is moved back... 
As always, check the rule book first!
That radius arm doesn't give me the warm fuzzies either. It looks like they were notched for tire clearance. If you look at the 'box member' at the rear of the floor pan, you should see 2 rubber plugs on either side of the driveshaft tunnel. Those are the radius arm mount points for the GT6 suspension meaning you can easily move the mount points inboard. You'd need to make new radius arms but that's not a big deal since there are already rod ends in place. It's not possible to really fark up the weird Spitfire suspension geometry any more than the factory did so I wouldn't be too concerned about that.
Early Spits had shorter axles and rear springs than the late cars so I'd say that's probably a late differential (4 mount bolts for the spring clamp, early diffs had 6) with most likely a GT6 rear spring. That was a common modification and would not be a true 'swing spring' unless someone did a good bit of custom work back there.
Swing spring or no, you are best off limiting the downward travel of the rear axles to lessen the massive camber change under braking that Spits are capable of. The easy way is to use shocks with shorter travel, IIRC there's a Corvette rear shock from the Stingray body style that's a nearly direct bolt on that will limit the travel. Or, I've seen travel limiters made from aircraft cable and even chains. You just don't want them to droop into the area occupied by other stuff like axles etc. From the pictures, it appears this may have already been done, which is A Good Thing.
also I really doubt I will find a MK1 body shell in better shape. As far as shocks, I was thinking about motorcycle shocks but I need to look at rules.
