For a stock carburated model, you're not going to notice any major difference. The car is super-light already and the stock brakes are fine.

Unfortunately, you're not going much faster for that little money. Your best bet will be to find a carburated browntop ZC to swap in, or a US D16A1 and the carb and manifold set from a carb'd browntop.

Swapping in the D15A3 Si 12v with all the fuel injection system will only net you 91 flywheel horsepower.