I'd start by doing a deep dive into the G3 platform. I don't pay a lot of attention to G3 engines but the factory has been pushing the 800 hp mark so if you can buy a car with a warranty with 800 hp in it, then I'd think that the at least 1000 would be fairly easy to reach. Don't know about 1200+, that would require talking to some experts.

Obviously you can also make 1200 with a G2 but it is a much cruder platform. Some people like that, some don't so it really comes down to personal taste. The G2 is probably a much easier resell path, not sure how big the market is for 1200 hp G3 engines.