Slowking would be better as a Special Wall but maybe it can work because Milotic is used a lot as a Mixed Wall mainly due to its high Special Defenses and HP. Slowking on the otherhand has the same HP but lower Special Defense, but it can work.
Slowbro and Snorlax would be easily hurt by Infernape. After a Nasty Plot it can OHKO Slowbro with Grass Knot and Close Combat Snorlax.
Hmm do you have any suggestions as to what wall could replace one of those two that ISN'T infernape weak?