Difference in X heads & J heads

Nothing outside of production tolerances or casting irregularities. X (894) head ports are said to flow a bit better. But the difference is minimal. Considering how the much sought after, old, worn and remachined 894 heads are over the years, machining a fresh 2.02" intake seat in a 1.88 J (915) or newer 360 head will provide as good or better results.