What follows is an attempt to design a GURPS version of the Gargun, discarding some things given in canon, and retaining others - all with intent to make a viable "alien" race.
Criteria I wish to preserve:
Gargun are generally, subsurface dwelling creatures, although there are exceptions to this. They are approximately 80 lbs in weight (depending on species) as adults, and are reasonably functionally intelligent (ie human level sentience). With a smaller mass in general, and a smaller cranium overall, the observation that animal like senses (such as a blood hound's sense of smell, or a cat's hearing) would not be the norm. In addition, the species engages in a form of egg laying for reproductive purposes, and that the egg must contain as much mass in nutrients, as the final "baby" form will have upon emerging from the egg. Thus, if the baby weighs 3 lbs in mass when born, it will need at least 3 lbs in nutrients for the egg itself.
From what I'm reading of the species, they are warm blooded, which means that their eggs need to be kept at a warm temperature instead of being left untended in colder regions - although one has to wonder what would happen if the eggs were in a somewhat cooler region.
They also enjoy a high level of instinctive behavior, termed "Genetic Memory". I don't know how GURPS would handle this overall, but I suspect that it will basically boil down to a given racial skill bonus for those creatures who have it. What follows will be the various steps I go through as I read GURPS SPACE on Alien Creation, and see where it gets me.