Sensitivity of Ilford Multigrade papers to the light spectrum changed throughout marks I to IV. You can find trace of this in their information sheets. More precisely, the suggested filter setting for colour heads varied from mark III to mark IV. I think that the mark IV pre-made filter set for B&W heads was updated and produced accordingly.
However, changes were quite small, and the basic concept remains the same: more yellow leads to soft contrast, more magenta leads to hard contrast. If I was you, I would just use the mark III filters and learn from the results: you would perhaps notice that grade "4" is most likely what you would usually call "3", but nothing worse than that. After all, variations in the head lamp spectrum can have a deeper influence on the results.
