i am thinking of converting a stegadon into an eldar exodite model to act either as a hq choice ridden by an autarch and a few crew or as a heavy support choice. What existing rules would i be able i use for either of these and do have any suggestions on modelling it? Help would be...

So I've had this model for a year or so now and just decided to paint him up. He's going to be used as my ancient carrying the engine of the gods so I wanted him to look older and grumbly haha. I hope you enjoy.