@ehaugw I handled the Pre Stich event here.
@jun2040 I created a model.json for my test block in addition to the other files. See here.
@blinky000 My models map a .png file to the sides of the block. See my .mtl file.
So I've made some substantial progress! I eventually found an OBJ test on the MC Forge Github (models, code), and my model now renders in-game! Unfortunately, the model is totally black (it's supposed to be bright yellow). If anyone has any insight as to why that may be, I'd appreciate it.
Attached are my model files in case those would be useful..
test_block.mtl
test_block.obj