360 mag with X heads anyone?

This thread is all over the place with guesses. I would suggest checking out the parts you have further so you know for sure what you are starting with before buying any parts to change things up.

That casting number can be a Magnum that has LA oiling holes drilled, which would allow an LA cam and cylinder head package with no oiling issues. You won't know for sure until you check it. If it has LA heads and rocker arms, just check for oil to the rocker arms. This is cleaner if done like a pre-lubing procedure, but can be done with engine running and a valve cover removed. If rockers are getting oil, engine is set up properly, which is very likely the case here.

Next, decide if you would be happy with the cost versus benefit of changing heads as you asked. Would you really see enough power increase to justify the cost of changing to an X head? If it has smog era 360 LA heads and you change to X heads with no camshaft upgrade, I doubt the cost would justify the effort and result.