I swap JDM D15B's all the time.
There's TONS of them floating around. Whenever someone's stock motor goes bad, a usual choice for their mechanic is to swap a jdm motor (much cheaper) in it.
How's your catalytic converter? Did you do a leakdown test?
The biggest problem with honda motors are people who run catless for more than two weeks, when this occurs, the exhaust valves start to warp ever so slightly, it still runs like a dream cuz it's a honda, but it'll always have high CO and will never pass NOx emissions. I'm not saying this is your problem, but it's a possibility.