Sarpedon has 8 legs. Spiders have eight legs too but they don't play 40k so that doesn't help much.
What I have to do is make Sarpedon's legs look convincing enough to suspend disbelief and have people accept that it's possible for this model to be "real." To do that, I'm borrowing a little spider anatomy. Spider legs are positioned a certain way off their bodies. It's not that everyone knows exactly how they are positioned, but most people know enough when they see something that's wrong. I just need to stay away from "wrong."
To get people to believe in the model, I need to make Sarpedon's legs look the part as much as possible. It's going to take some conversion work, but it's not impossible.
The real trick is going to be how I make 8 legs "fit" around his torso. It looks like 6 is the maximum for actual space so it's going to be interesting. In the picture above, you can see that the four on the left side go past the mid point and start to take up space where the other four would need to go.
I wish I'd posted this much earlier and gotten all the great input you guys have. Even though this stage is already complete, I want to thank you guys for all the comments and help, it's much appreciated!
Here's what I ended up doing to solve the problem:
Each leg is tapered down to fit. I've got four legs on each side. He stands on the back three and both front legs are up in the air. The right front leg is the bionic one. It's magnetised so it can be removed and used as a wound counter (it's a two-wound model).
My Project Link: Follow my Sarpedon Conversion