Assuming that the timing chain was installed correctly (dot to dot) and you said it starts and idles fine, then the distributor may just be a tooth "off" when it was dropped in the block. If it was 180 degrees off I don't think it would run without a lot of spitting and popping/backfiring. If the timing chain gears weren't aligned correctly, then you may have artificially retarded it, causing it to run sluggish. Make sure you don't have any vacuum leaks either.