Quick... which way's better (225/273)

Regardless of what the crowd says, it's always easier and more affordable to leave a car with the type engine it came with. That said, 300HP is a tall order for any slant 6 that doesn't have a blower or turbo. I have one on the stand now that MIGHT reach out and touch it, but it has a head that has had 318 valves put in it, it's been ported big time and the rest of the engine is far from stock. Even with all that, I would be very shocked if I got 300HP. But I'm not going for a number. I'm going to have fun. Remember, these cars are light. They don't need a crap load of power to be fun.