Second post corrects my error but it would be like this.
{
"textures": {
"0": "cammod:blocks/Ancient_side",
"1": "cammod:blocks/AncientGrass",
"2": "cammod:blocks/AncientGrass_bottom"
},
"elements": [
{
"name": "Cube",
"from": [ 0.0, 0.0, 0.0 ],
"to": [ 16.0, 16.0, 16.0 ],
"faces": {
"north": { "texture": "#0", "uv": [ 0.0, 0.0, 16.0, 16.0 ] },
"east": { "texture": "#0", "uv": [ 0.0, 0.0, 16.0, 16.0 ] },
"south": { "texture": "#0", "uv": [ 0.0, 0.0, 16.0, 16.0 ] },
"west": { "texture": "#0", "uv": [ 0.0, 0.0, 16.0, 16.0 ] },
"up": { "texture": "#1", "uv": [ 0.0, 0.0, 16.0, 16.0 ] },
"down": { "texture": "#2", "uv": [ 0.0, 0.0, 16.0, 16.0 ] }
"particle": "modid:blocks/texturename"
}
}
]
}[/font]