Creatures Caves

Yes, in c3, the equivalent to the Sandrabellum are the "Floating Receptor-Emitter" loci.

In your receptor and emitter genes for c3, to make equivalents of genes that would talk to the C2 Sandrabellum, you would attach them to:
Organ:Creature
Tissue:Circulatory

These loci will act exactly the same as the cells of the Sandrabellum. There are 32 of them numbered 0-31...
As far as I can tell, the base genome uses only 0-22.

23-31 should be free for any additional custom receptors and emitters to attach to (so, you would choose 'creature, circulatory, floating recep-emit 23' for the Locus in the Testosterone receptor and Inhibin emitter, instead of 'brain, lobe 9, cell 5').

As for the receptor for Inhibin, which slows down the gonad, you should be able to use it as listed. So, if I understand the whole reaction right, the creature produces Inhibin when it has a very high level of Testosterone, which is received by the gonad and slows down it's production of sex hormones to help lower the level to something more reasonable.

I believe that Kezune made a type of c3 norn that uses Inhibin... I'm not sure what she did exactly, it may or may not involve these receptors and emitters... but you may want to look at what she did (I think it's the CFE Gizmo genome).

This architecture is more realistic too, since now the action of those chemical emitters and receptors are linked to the circulatory system, which makes sense since these regulatory loci and chemicals like Inhibin serve the function of real glands and hormones in the creature. The loci detect and emit chemicals that are distributed in the creature's bloodstream which can affect their various organs, including their brain. A creature who has a bad heart or poor circulation would not distribute chemicals well throughout its body, and we see the same exact thing with real animals.

EDIT: Okay, I spotted something weird... probably another error in C3 genome in kind of copying what is in C2 then adding to it haphazardly...

In C3... There is a testosterone receptor at floating emitter-receptor locus 5... (interesting how it's the same loci number as in c2...) But... there is no corresponding emitter (this is where inhibin would be produced)... Instead there is another receptor-emitter pair which is also attached to locus 5, which regulates turning hunger for carbs into hunger for carb stress... This means that male C3 creatures actually get hunger for carb stress from high levels of testosterone, instead of producing inhibin... (very weird...)

SECOND EDIT: That's very bad actually... the gonad's receptors for stress increase chance and degree of mutation... so not only do male creatures overproduce testosterone, this increases their mutation rate and make bad mutations more likely... And this is just the gonad... Stress has a bad effect on most of their body... since they are always producing testosterone while fertile, all of their organs are under constant stress. So, male cretures need a constant supply of carbs even when they are not hungry, or this stress will build up to toxic levels and stay in their systems forever.

The fix would be to take that broken and currently unused receptor for testosterone (gene 210 in most, Receptor #69...) and change the locus to the unused floating receptor-emitter 23 where it will not harm the creature.

Since the receptor as it is does nothing but produce toxic levels of stress anyway, and that locus is unused, this will have no ill effect. You can then add an emitter for inhibin attached to that locus if you wish.