De-stroke an ALH 20mm, which gives 1499cc, and carry on with well known power enhancement mods. Done. This has already been posted in this thread before. No sleeving nonsense or exotic, unobtanium methods.
300 HP is not out of the realm of possibility.
Edit:
- Ported big valve ALH head and 11mm lift race cam from NPS heads
- 12mm pump / 11mm cam plate, .360 injectors
- Compound turbo (you'll need about 48 PSI of boost for 300 HP @ 1.5L displacement; impossible to generate this efficiently in a single stage)
How about the above but start with a PD engine?
PD Nozzles cost a bit more but mean no spending on a big pump.
Then as it's a speed record car with the right gear ratios does it actually need compounding or would a big hybrid VNT eg Darkside GTD2872VRK provide enough boost in the airflow range required and with it being de-stroked up the rpm to ~5500 to make the power?
With the right injectors and some good exhaust manifold cooling you could run a lot of fuel e:g smoke haze even when on boost. This is based on the assumption that the engine only has to run ~50 miles total so exhaust manifold cracking from excessive heat and heat cycling isn't a major concern and the GTD vane pack should be resilient to hot temperatures ~950c?