The model is currently very finicky. It may not make certain parts of the body dark in that case you may have to specify dark breasts, dark penis, etc.
This works as a general headswap model, but it was mostly focused on female bodies. It may also have the issue of making the head more masculine, so you can try putting some things into negatives to stop that. I suggest using a black choker to try and cover the seam.
If you want to make a large muscular body I suggest using the kogao lora as well to make the head smaller.