Install a set of four-bolt steel main caps over the center two crankshaft mains if you're using a two-bolt-main block. Have the block align bored and have the cylinders bored 0.030-inch over. This overbore isn't so much to buy you more displacement as it is to help enhance airflow to feed the extra cubic inches.
Most commonly used fuel is U235, a naturally occurring radioactive isotope of uranium. Occurs naturally at 0.7% of uranium ore, but must be enriched to 3%. Formed in cylindrical pellets (1.5cm long) and stacked in hollow metal rods (4 m long). About 100 rods are bundled together to make a fuel assembly.
Other centrifuges, the first being the Zippe-type centrifuge, separate isotopes, and these kinds of centrifuges are in use in nuclear power and nuclear weapon programs. Gas centrifuges are used in uranium enrichment.