I prefer to call it a 5.9 Mag, it is enough different to have its own name. For one thing, the external balance is different.

If you are using an automatic, then you use the stock 5.9 Mag flexplate and a neutral balance converter. Mags carry the imbalance on the flexplate, 360s have the imbalance on the converter. [5.2 Mags are internally balanced, as are all 318s.]
If you will use the converter from behind a an LA 360, the imbalance weights must be removed, and the 5.9 Mag flexplate used.

R.