That's an interesting take on the riastradh. I must admit I wasn't too sure when I saw the donor figure but even just with the head conversion, it's already working out nicely.
I don't see how you could portray this "contorted limbs" thing without it looking silly (attempts by Belardinelli and Fabry notwithstanding, those were awesome in their weirdness), especially in miniature form. I've got the warped Slaíne by Foundry and I must say I'm inclined to prefer your take already.