Rapid prototyping may be an opportunity to build new WWII engines from scratch. RR Griffons? Napier Sabres? P&W R2800s? What fun! You will have to solve once again, all sorts of reliability and production problems that were solved during WWII. All those guys flying Curtis C-46s will thank you. Otherwise, you have serious engineering costs to amortise over a short production run. Hopefully, some billionaire is determined to fly his Hawker Typhoon and Tempest.
Is it worthwhile developing a new internal combustion engine? Power is the product of displacement, Mean Effective Pressure (MEP), and RPMs. MEP ultimately is controlled by your fuel octane number, which is taken advantage of by your supercharger and your compression ratio. RPM is mostly a function of how long you want your bearings to last. Modern technology might make your engine more fuel efficient, but nobody cares about that in air racing.
How long is an unlimited air racer required to run? A cooling system completely inadequate for a WWII P-51 Mustang mission, may last long enough to win an air race.