I’ve been following S-Tai for a good while. You won’t find much info on Super Taikyu entries that are non-homologated race cars. You’ll have to search Japan sites related to those cars. Some independent write ups have bits of info. An estimate of power or approximate weight. The teams that run the cars rarely post info. Lots of Google translate.
The ST-2 class of cars have enough modifications for safety and not much in terms of engine power modifications. They’re pretty close to stock.
Hopefully, some specs are mentioned here.