The rules for a sport car in my opinion is convertible, manual gearbox, low to the ground and very small and feel like it is fast.
Honda S600 was almost perfect as the problem with 90% of cars are they feel slow at the speed limit, but not so the Honda, you had to wring it out in every gear just to get to the limit and it felt like it was doing 200kph when doing 100kph. Pity during the time I owned it I spent 90% of the time fixing it and only 10% driving it.
My first real car and the car I learnt to drive in was a Honda S800 coupe, they were really amazing cars not that reliable but could rev to about 8-9k rpm........very much in vogue again and going for ridiculously serious money if you can find a good one without rust.
regards