Having a ton of thoughts on this... But now I'm wondering if the pre ~1975 exemption vehicles could basically be like surrogates for all the current engines and mods we love. Think about it, people buy up whatever cars pre 1975, doesn't even have to be a Mustang, Coyote swap a '55 Cadillac, GT500 swap a 1960 Dodge truck, ZR1 swap a 1966 Corvette. That way you get all the modern advancements of the newer engines, the mods are already a plenty out in the marketplace even if they stop being produced now, and you skirt emissions! Lmao
Right now everything over 25 years old is emissions exempt. That is why R32 and R33 GTRs are being bought up right now. I have yet to hear if that is going to change.