After much trial and error I have now removed the top four leaves from the rear spring (Vitesse donor), and fitted 150lb Spitfire springs to the front, cut down by 1.5 coils, with new, standard dampers all round.
This gave it a suitable ride height with no lowering block needed and great ride and handling as the tyres now stay on the road instead of hopping about all over the place, which they did with stiffer springs fitted.
As for the brakes, I've got standard drums at the back with grooved, solid discs up front and an aftermarket servo for better feel.
Bearing in mind I have a cast-iron six pot up front, that setup is plenty powerful enough for fast road use. Can't comment on track use as I don't do track days, but Phil J (green Spyder No.2 above) is competitive with early 911's on the track and has standard Vitesse brakes and about 130bhp from his 2.5 six.
Not sure how much modification the Spitfire running gear will need, but I wouldn't think it will take much fettling to make it a mighty fast car.
Good luck.
