Well, thats an odd question. Are you sure you know what conversion means? You can convert everything mentioned by n810. It's just about ideas... You need to have something in your mind first... You can get some inspiration throughout threads on this forum. For example you can convert the Skink Chief on Horned-one (there is no original model for him except that old ragiment of renown ones)... Making one will surely be a conversion
Are you planning on playing with that? Because a Skink Chief can't legally be mounted on a carnosaur, plus that would probably just look plain silly.
He definitely can. Just make sure it's modeled to have everything that the Stegadon would have and nothing that it wouldn't. For instance, you'd have to think of some way to put all the Skink crew members on the back of the Carnosaur, as well as the Stegadon's weapon. And don't forget to use the right base size! I look forward to seeing what you come up with - it sounds cool1