Here's my progress on Issac so far.
Curiously, it didn't seem that Fat Cat's an Issac's body were that much different from one-another in terms of proportions. I managed to easily strip off Fat Cat's body and use a duplicate of it as Issac's own body, albeit with a few minor adjustments such as giving Issac's body a more pear-shaped look from the brute force cube body of Fat Cat. I also changed the shape of the shoes and the fingers.
The head, I realize, is cut off around the bottom of the eyes. There's a reason for that. Throughout the trailer, Issac wears a helmet and goggles which covers the top half of his head which means there won't be much need, nor much point in me modelling the rest of the head.