https://www.thingiverse.com/thing:3775784

This model has been hard to find but here it is it's a scan stl model of the original costume head from the old series.

https://www.thingiverse.com/thing:1284588

You can convert these with the free spin3d program it's a free 3d format translator that can convert the sto files to obj then just do a head replacement or patent the obj to a figure you morphed with the morph brush, I recommend you use map maker to create a texture template to make a texture these models don't have any textures.

I used photos to create textures for Michial 4 still working on the figures I have to create hand claws and feet still.

Basically all you need to do is smooth out the muscle from the human figure you use so there's no sign of muscle in the legs and arms make the joints thicker the body and limbs flatter with allot less muscle curvature once you do that you will have either make hands and feet or take the figure into Z-Brush and resculpt it there with hands and feet for a much better result.

You can can fix the sleestack head with the shoulders by using the grouping tool to block out the shoulders to make tranz-map to hide all that, then make a lizard collier from a flat round circle you can sculpt it to fit with the morph brush then tranz map then edges and add a scale texture to the lizard frill which will help hide the some issues with head replacement.

Some interesting info in this thread !