2. Hot cams and headers and (ideally) and chip with a tune just for this setup. The M3 cams would be the hot cams for the m50 engines.
3. Top overhaul with decarbonisation of the head.
4. Turbo or supercharging.
5. Change of rear differential to ratios which improve low end acceleration.
6. Engine transplant.
But frankly, its better to save the money.