IMO 004 and 006 needs a smooth running high reving quad cam motor, possibly even a 12, if youre building a euro inspired and driving car it needs a euro style motor.. Its the smoothness and revability of an ohc motor that works for these types of cars, otherwise its sorta like a vette or a modern rendition of the intermechanica from the early 70s. The question boils down to who builds a Na quad cam motor thats emissions certified. Ford we know does with both the mustang Gt and Gt 350. I think cosworth does an emisisons friendly version of the ford, which adds provenance and performance. The Aston V12 if the motor is still in production? I wonder if Lambo would sell Jim some Aventador 12's. Still I would talk to mercury marine about emissions certifying their motor. Much as i love a SBC it just seems the wrong motor for these otherwise well sorted and excellent cars. But then maybe the price is super reasonable. Or maybe Jim is prepared to sell a roller, and then we can install our own motor. Perhaps possibly with the impending demise of the 750 hp zr1 motor and the vette moving to quad cam these older SBC will be able to carry the classic moniker for these cars. But still one could just get a zr1.