So I went ahead and followed the guides you've written as well as the bits of advice in this forum and I've managed to get the neptune_swimgear model working with sounds and actions :)

It's a complete hack job, really just grabbing the exp, snds and mtns from your neptune folder.. but hey it works haha

One thing though..

The error {"name": "belly", "id": "D_REF.PT_BELL"}
is still in the released program here. I'm not sure whether the Y should be added in the neptune_swimwear.model.json or just left as BELL? I've tried with and without the Y and it seems to work exactly the same either way which is odd!

I'd quite like to make other models work but I can't figure out how you managed to figure out which mtns were which from the decrypted APK. All the mtns are named virtually the same from what I can see. Just number differences.