Unable to apply textures to custom model

I am trying to add a custom parent model to use in a block. I made the model in Blockbench, it is a cube model with two sets of textures: one for "front" (interchangable for the different variants of the block) and one for all remaining sides (fixed for all variants). 

I can import it into MCreator and assign all texture mappings in the resources tab just fine (all texture slots show up) but whenever I try to use that model for a block I can only apply the main/bottom texture. I can't find any info on this and have no idea what I'm doing wrong. Any help would be appreciated.